:double sad face:

With JDK8:

```
[INFO] Compiling 7 source files to /opt/jruby/core/target/classes
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO] 
[INFO] JRuby .............................................. SUCCESS [  2.043 s]
[INFO] JRuby Core ......................................... FAILURE [ 11.543 s]
[INFO] JRuby Lib Setup .................................... SKIPPED
[INFO] JRuby Integration Tests ............................ SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 35.618 s
[INFO] Finished at: 2019-04-03T09:47:10Z
[INFO] Final Memory: 58M/172M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.3:compile (anno) on project jruby-core: Compilation failure -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
[ERROR] 
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <goals> -rf :jruby-core
```