Add a hack for the broken JavaVersion enum in Gradle. It returns vers…

…ion "1.9" and "1.10" (which are invalid targetCompatibility versions) and this problem is only fixed after Java 11. Before Java 11 we switch to plain "majorVersion" property. This closes #143

src/main/resources/de/thetaphi/forbiddenapis/gradle/plugin-init.groovy

@@ -60,7 +60,9 @@ project.sourceSets.all{ sourceSet ->
       }
       classesDirs = { getSourceSetClassesDirs() }
       classpath = { sourceSet.compileClasspath }
-      targetCompatibility = { project.targetCompatibility?.toString() }
+      // Gradle is buggy with it's JavaVersion enum: We use majorVersion property before Java 11 (6,7,8,9,10) and for later we use toString() to be future-proof:
+      targetCompatibility = { (project.targetCompatibility?.hasProperty('java11Compatible') && project.targetCompatibility?.java11Compatible) ?
+        project.targetCompatibility.toString() : project.targetCompatibility?.majorVersion }
     }
     // add dependency to compile task after evaluation, if the classesDirs collection has overlaps with our SourceSet:
     project.afterEvaluate{