diff --git a/package.json b/package.json
index dedde48..a47759e 100644
--- a/package.json
+++ b/package.json
@@ -20,7 +20,7 @@
   "license": "CC-BY-4.0",
   "devDependencies": {
     "ava": "^0.22.0",
-    "eslint": "^4.9.0",
+    "eslint": "^4.18.2",
     "eslint-config-airbnb-base": "^12.1.0",
     "eslint-plugin-import": "^2.7.0",
     "grunt": "~0.4.5",
diff --git a/yarn.lock b/yarn.lock
index 46ea204..39f8154 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -58,9 +58,9 @@ acorn@^3.0.4:
   version "3.3.0"
   resolved "https://registry.yarnpkg.com/acorn/-/acorn-3.3.0.tgz#45e37fb39e8da3f25baee3ff5369e2bb5f22017a"
 
-acorn@^5.1.1:
-  version "5.1.2"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.1.2.tgz#911cb53e036807cf0fa778dc5d370fbd864246d7"
+acorn@^5.5.0:
+  version "5.7.3"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.3.tgz#67aa231bf8812974b85235a96771eb6bd07ea279"
 
 ajv-keywords@^2.1.0:
   version "2.1.0"
@@ -73,18 +73,9 @@ ajv@^4.9.1:
     co "^4.6.0"
     json-stable-stringify "^1.0.1"
 
-ajv@^5.1.0:
-  version "5.2.3"
-  resolved "https://registry.yarnpkg.com/ajv/-/ajv-5.2.3.tgz#c06f598778c44c6b161abafe3466b81ad1814ed2"
-  dependencies:
-    co "^4.6.0"
-    fast-deep-equal "^1.0.0"
-    json-schema-traverse "^0.3.0"
-    json-stable-stringify "^1.0.1"
-
-ajv@^5.2.0, ajv@^5.2.3:
-  version "5.3.0"
-  resolved "https://registry.yarnpkg.com/ajv/-/ajv-5.3.0.tgz#4414ff74a50879c208ee5fdc826e32c303549eda"
+ajv@^5.1.0, ajv@^5.2.3, ajv@^5.3.0:
+  version "5.5.2"
+  resolved "https://registry.yarnpkg.com/ajv/-/ajv-5.5.2.tgz#73b5eeca3fab653e3d3f9422b341ad42205dc965"
   dependencies:
     co "^4.6.0"
     fast-deep-equal "^1.0.0"
@@ -878,7 +869,7 @@ chalk@^1.1.1, chalk@^1.1.3:
     strip-ansi "^3.0.0"
     supports-color "^2.0.0"
 
-chalk@^2.0.0, chalk@^2.1.0:
+chalk@^2.0.0, chalk@^2.0.1, chalk@^2.1.0:
   version "2.3.0"
   resolved "https://registry.yarnpkg.com/chalk/-/chalk-2.3.0.tgz#b5ea48efc9c1793dccc9b4767c93914d3f2d52ba"
   dependencies:
@@ -886,14 +877,6 @@ chalk@^2.0.0, chalk@^2.1.0:
     escape-string-regexp "^1.0.5"
     supports-color "^4.0.0"
 
-chalk@^2.0.1:
-  version "2.1.0"
-  resolved "https://registry.yarnpkg.com/chalk/-/chalk-2.1.0.tgz#ac5becf14fa21b99c6c92ca7a7d7cfd5b17e743e"
-  dependencies:
-    ansi-styles "^3.1.0"
-    escape-string-regexp "^1.0.5"
-    supports-color "^4.0.0"
-
 chokidar@^1.4.2:
   version "1.7.0"
   resolved "https://registry.yarnpkg.com/chokidar/-/chokidar-1.7.0.tgz#798e689778151c8076b4b360e5edd28cda2bb468"
@@ -1216,11 +1199,11 @@ debug@^2.1.3, debug@^2.2.0, debug@^2.6.3, debug@^2.6.8:
   dependencies:
     ms "2.0.0"
 
-debug@^3.0.1:
-  version "3.1.0"
-  resolved "https://registry.yarnpkg.com/debug/-/debug-3.1.0.tgz#5bb5a0672628b64149566ba16819e61518c67261"
+debug@^3.1.0:
+  version "3.2.6"
+  resolved "https://registry.yarnpkg.com/debug/-/debug-3.2.6.tgz#e83d17de16d8a7efb7717edbe5fb10135eee629b"
   dependencies:
-    ms "2.0.0"
+    ms "^2.1.1"
 
 decamelize@^1.0.0, decamelize@^1.1.1, decamelize@^1.1.2:
   version "1.2.0"
@@ -1293,12 +1276,11 @@ doctrine@1.5.0:
     esutils "^2.0.2"
     isarray "^1.0.0"
 
-doctrine@^2.0.0:
-  version "2.0.0"
-  resolved "https://registry.yarnpkg.com/doctrine/-/doctrine-2.0.0.tgz#c73d8d2909d22291e1a007a395804da8b665fe63"
+doctrine@^2.1.0:
+  version "2.1.0"
+  resolved "https://registry.yarnpkg.com/doctrine/-/doctrine-2.1.0.tgz#5cd01fc101621b42c4cd7f5d1a66243716d3f39d"
   dependencies:
     esutils "^2.0.2"
-    isarray "^1.0.0"
 
 dom-serializer@0:
   version "0.1.0"
@@ -1429,32 +1411,36 @@ eslint-scope@^3.7.1:
     esrecurse "^4.1.0"
     estraverse "^4.1.1"
 
-eslint@^4.9.0:
-  version "4.9.0"
-  resolved "https://registry.yarnpkg.com/eslint/-/eslint-4.9.0.tgz#76879d274068261b191fe0f2f56c74c2f4208e8b"
+eslint-visitor-keys@^1.0.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/eslint-visitor-keys/-/eslint-visitor-keys-1.1.0.tgz#e2a82cea84ff246ad6fb57f9bde5b46621459ec2"
+
+eslint@^4.18.2:
+  version "4.18.2"
+  resolved "https://registry.yarnpkg.com/eslint/-/eslint-4.18.2.tgz#0f81267ad1012e7d2051e186a9004cc2267b8d45"
   dependencies:
-    ajv "^5.2.0"
+    ajv "^5.3.0"
     babel-code-frame "^6.22.0"
     chalk "^2.1.0"
     concat-stream "^1.6.0"
     cross-spawn "^5.1.0"
-    debug "^3.0.1"
-    doctrine "^2.0.0"
+    debug "^3.1.0"
+    doctrine "^2.1.0"
     eslint-scope "^3.7.1"
-    espree "^3.5.1"
+    eslint-visitor-keys "^1.0.0"
+    espree "^3.5.2"
     esquery "^1.0.0"
-    estraverse "^4.2.0"
     esutils "^2.0.2"
     file-entry-cache "^2.0.0"
     functional-red-black-tree "^1.0.1"
     glob "^7.1.2"
-    globals "^9.17.0"
+    globals "^11.0.1"
     ignore "^3.3.3"
     imurmurhash "^0.1.4"
     inquirer "^3.0.6"
     is-resolvable "^1.0.0"
     js-yaml "^3.9.1"
-    json-stable-stringify "^1.0.1"
+    json-stable-stringify-without-jsonify "^1.0.1"
     levn "^0.3.0"
     lodash "^4.17.4"
     minimatch "^3.0.2"
@@ -1468,7 +1454,7 @@ eslint@^4.9.0:
     semver "^5.3.0"
     strip-ansi "^4.0.0"
     strip-json-comments "~2.0.1"
-    table "^4.0.1"
+    table "4.0.2"
     text-table "~0.2.0"
 
 espower-location-detector@^1.0.0:
@@ -1480,11 +1466,11 @@ espower-location-detector@^1.0.0:
     source-map "^0.5.0"
     xtend "^4.0.0"
 
-espree@^3.5.1:
-  version "3.5.1"
-  resolved "https://registry.yarnpkg.com/espree/-/espree-3.5.1.tgz#0c988b8ab46db53100a1954ae4ba995ddd27d87e"
+espree@^3.5.2:
+  version "3.5.4"
+  resolved "https://registry.yarnpkg.com/espree/-/espree-3.5.4.tgz#b0f447187c8a8bed944b815a660bddf5deb5d1a7"
   dependencies:
-    acorn "^5.1.1"
+    acorn "^5.5.0"
     acorn-jsx "^3.0.0"
 
 esprima@^2.6.0:
@@ -1518,7 +1504,7 @@ esrecurse@^4.1.0:
     estraverse "^4.1.0"
     object-assign "^4.0.1"
 
-estraverse@^4.0.0, estraverse@^4.1.0, estraverse@^4.1.1, estraverse@^4.2.0:
+estraverse@^4.0.0, estraverse@^4.1.0, estraverse@^4.1.1:
   version "4.2.0"
   resolved "https://registry.yarnpkg.com/estraverse/-/estraverse-4.2.0.tgz#0dee3fed31fcd469618ce7342099fc1afa0bdb13"
 
@@ -1882,7 +1868,11 @@ global-dirs@^0.1.0:
   dependencies:
     ini "^1.3.4"
 
-globals@^9.17.0, globals@^9.18.0:
+globals@^11.0.1:
+  version "11.12.0"
+  resolved "https://registry.yarnpkg.com/globals/-/globals-11.12.0.tgz#ab8795338868a0babd8525758018c2a7eb95c42e"
+
+globals@^9.18.0:
   version "9.18.0"
   resolved "https://registry.yarnpkg.com/globals/-/globals-9.18.0.tgz#aa3896b3e69b487f17e31ed2143d69a8e30c2d8a"
 
@@ -2661,6 +2651,10 @@ json-schema@0.2.3:
   version "0.2.3"
   resolved "https://registry.yarnpkg.com/json-schema/-/json-schema-0.2.3.tgz#b480c892e59a2f05954ce727bd3f2a4e882f9e13"
 
+json-stable-stringify-without-jsonify@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/json-stable-stringify-without-jsonify/-/json-stable-stringify-without-jsonify-1.0.1.tgz#9db7b59496ad3f3cfef30a75142d2d930ad72651"
+
 json-stable-stringify@^1.0.1:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/json-stable-stringify/-/json-stable-stringify-1.0.1.tgz#9a759d39c5f2ff503fd5300646ed445f88c4f9af"
@@ -2994,6 +2988,10 @@ ms@2.0.0, ms@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/ms/-/ms-2.0.0.tgz#5608aeadfc00be6c2901df5f9861788de0d597c8"
 
+ms@^2.1.1:
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/ms/-/ms-2.1.2.tgz#d09d1f357b443f493382a8eb3ccd183872ae6009"
+
 multimatch@^2.1.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/multimatch/-/multimatch-2.1.0.tgz#9c7906a22fb4c02919e2f5f75161b4cdbd4b2a2b"
@@ -4095,7 +4093,7 @@ symbol-observable@^1.0.4:
   version "1.0.4"
   resolved "https://registry.yarnpkg.com/symbol-observable/-/symbol-observable-1.0.4.tgz#29bf615d4aa7121bdd898b22d4b3f9bc4e2aa03d"
 
-table@^4.0.1:
+table@4.0.2:
   version "4.0.2"
   resolved "https://registry.yarnpkg.com/table/-/table-4.0.2.tgz#a33447375391e766ad34d3486e6e2aedc84d2e36"
   dependencies:
@@ -4523,7 +4521,7 @@ xdg-basedir@^3.0.0:
   version "3.0.0"
   resolved "https://registry.yarnpkg.com/xdg-basedir/-/xdg-basedir-3.0.0.tgz#496b2cc109eca8dbacfe2dc72b603c17c5870ad4"
 
-xmldom@~0.1.27:
+xmldom@^0.1.27, xmldom@~0.1.27:
   version "0.1.27"
   resolved "https://registry.yarnpkg.com/xmldom/-/xmldom-0.1.27.tgz#d501f97b3bdb403af8ef9ecc20573187aadac0e9"