Generate solution task up-to-date fix (#138)

## Description
GenerateSolution task was being up-to-date even though it has no inputs and it wasn't meant to be. This happens because of inherited inputs from its parent class.

Ps: this PR is forked from #137 

## Changes
* ![FIX] GenerateSolution now is never up-to-date

src/integrationTest/groovy/wooga/gradle/unity/tasks/GenerateSolutionTaskIntegrationSpec.groovy

@@ -20,6 +20,21 @@ class GenerateSolutionTaskIntegrationSpec extends UnityTaskIntegrationSpec<Gener
         res.standardOutput.contains("-executeMethod UnityEditor.SyncVS.SyncSolution")
     }
 
+
+    @UnityPluginTestOptions(addMockTask = false, disableAutoActivateAndLicense = false)
+    def "generateSolution task is never up-to-date"() {
+        given: "applied atlas-unity plugin"
+
+        when: "generateSolution task is called"
+        def firstRes = runTasksSuccessfully("generateSolution")
+        and: "generateSolution task is called again"
+        def secondRes = runTasksSuccessfully("generateSolution")
+
+        then: "neither of ran tasks were up-to-date"
+        !firstRes.wasUpToDate(":generateSolution")
+        !secondRes.wasUpToDate(":generateSolution")
+    }
+
     @Requires({ os.macOs })
     @UnityPluginTestOptions(unityPath = UnityPathResolution.Default)
     @UnityInstallation(version = "2019.4.24f1", cleanup = false)

src/integrationTest/groovy/wooga/gradle/unity/tasks/TestTaskIntegrationSpec.groovy

@@ -407,5 +407,4 @@ class TestTaskIntegrationSpec extends UnityTaskIntegrationSpec<Test> {
                 taskResult.args.contains("-debugCodeOptimization")
 
     }
-
 }

src/main/groovy/wooga/gradle/unity/tasks/GenerateSolution.groovy

@@ -5,6 +5,7 @@ import wooga.gradle.unity.UnityTask
 class GenerateSolution extends UnityTask {
 
     GenerateSolution() {
+        outputs.upToDateWhen { false }
         executeMethod = "UnityEditor.SyncVS.SyncSolution"
     }
 }