Update travis and tests configuration

Travis no longer supports PHP 5.4 on the default machine, so this
updates that and tests some newer version as well. A little bit of a
workaround is required to test PHP 7

.travis.yml

@@ -1,18 +1,19 @@
+dist: trusty
 language: php
 
 php:
-    - 5.4
     - 5.6
+    - 7.1
 
 env:
     - WP_VERSION=latest WP_MULTISITE=0
     - WP_VERSION=latest WP_MULTISITE=1
-    - WP_VERSION=3.8 WP_MULTISITE=0
-    - WP_VERSION=3.8 WP_MULTISITE=1
+    - WP_VERSION=4.0 WP_MULTISITE=0
+    - WP_VERSION=4.0 WP_MULTISITE=1
 
 before_script:
     - composer self-update
     - composer install --prefer-source --no-interaction --dev
-    - bash bin/install-wp-tests.sh wordpress_test root '' localhost $WP_VERSION 
+    - chmod +x tests/init.sh && bash tests/init.sh $TRAVIS_PHP_VERSION $WP_VERSION
 
 script: phpunit

tests/init.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+TRAVIS_PHP_VERSION=${1-0}
+WP_VERSION=${2-latest}
+
+echo "[init-tests.sh] TRAVIS_PHP_VERSION=$TRAVIS_PHP_VERSION"
+echo "[init-tests.sh] WP_VERSION=$WP_VERSION"
+
+# PHP 7 is incompatible with WordPress v4 and lower so we force WordPress 5.0
+if [[ $TRAVIS_PHP_VERSION == "7.1"* && $WP_VERSION == 4.0 ]]; then
+    echo "[notice] PHP 7 is incompatible with WordPress v4 and lower. Forcing WordPress 5.0."
+    WP_VERSION=5.0
+else
+    :
+fi
+
+echo "[init-tests.sh] Using WP_VERSION $WP_VERSION"
+
+bash bin/install-wp-tests.sh wordpress_test root '' localhost $WP_VERSION