Changed testJava() to allow Java 8

This is a simple change that allows it to run with Java 8. Not 100% sure about Java 8 support, but it seems stable to the extent I've used it.

Also wasn't sure how to compile the ClosureCompiler.min.js file, or even if that's part of a build process/etc. Sorry if I missed that in the docs. For what it's worth, it's done with `SIMPLE_OPTIMIZATIONS`.