scalastyle 0.5.0 (new formula)

Scalastyle is a style checker for Scala. They have a CLI interface and there
have been requests to make it available as a Homebrew formula:
  https://github.com/scalastyle/scalastyle-batch/issues/1

Here is such a formula. :)
Can this test be modified to do something more substantial then e.g. `--version` or `--help`? See `cmake.rb` for an example of a formula with a good test. Thanks!