Don't fail on coverage drop, it breaks 'rvm all do' tests.
Refactor for better compatibility and less deps.

- always pass environment manually
- use backticks instead of Mixlib::ShellOut for jruby
- MiniGit#git just returns the return value of the system() call

JRuby works!
Merge branch 'feature/jruby_support' into develop
Version 0.0.2
Merge branch 'release/0.0.2'