Remove the test directory

Seeing as how there's nothing actually in it...
Merge remote-tracking branch 'upstream/master'
Use Gem::Requirement for checking versions
Merge pull request #68 from kejadlen/remove-test-dir

Remove the unused test directory
Merge pull request #69 from kejadlen/rubygems-version

Use Gem::Requirement.new to compare versions
Refactor / simplify Guard::Minitest::Inspector
Update Changelog