jruby-gradle-jar-plugin is walking upright

In this changeset:
+ Jar task type extended with `jruby` closure
+ Ability to add custome gem directories
+ Ability to make a JAR executable using `warbler-bootstrap`
+ Ability to make A JAR executable supplying own main class
I have noticed that when GEMs get extracted and the packed into the JAR again, wgen are probably adding a number of files which has no bearing on final usage. 

With my limited Ruby knowledge I could be wrong, but I would think we do not need to pack `cache` or `test` again.