Does not compile with Java 11

[Serranya]

The current master branch fails when compiled with Java11:

[...]
[INFO] Reactor Summary for rocker 1.2.1-SNAPSHOT:
[INFO] 
[INFO] rocker ............................................. SUCCESS [  4.852 s]
[INFO] rocker-runtime ..................................... SUCCESS [  6.012 s]
[INFO] rocker-compiler .................................... SUCCESS [  7.292 s]
[INFO] rocker-maven-plugin ................................ SUCCESS [  3.267 s]
[INFO] rocker-gradle-plugin ............................... FAILURE [  5.523 s]
[INFO] rocker-test-java6 .................................. SKIPPED
[INFO] rocker-test-reload ................................. SKIPPED
[INFO] rocker-test-java8 .................................. SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  27.544 s
[INFO] Finished at: 2018-12-19T09:42:43+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.fortasoft:gradle-maven-plugin:1.0.8:invoke (gradle-clean) on project rocker-gradle-plugin: Execution gradle-clean of goal org.fortasoft:gradle-maven-plugin:1.0.8:invoke failed: Could not determine java version from '11.0.1'. -> [Help 1]
[...]

[jjlauer]

Hey @Serranya -- reviewing your PR now. mvn test was running fine -- I finally figured out mvn clean is where that gradle + java 11 issue comes into play. I'm not a gradle expert -- if we bump up the dependency from 3.5 to 5 will that break users from using the gradle plugin running on gradle version < 5?

[Serranya]

@jjlauer The PR was made by someone else and not by me. I don't use gradle.

[volyx]

Is it about this PR #99?