add basic test suite

Hi there! :wave: 

I was looking for just this code when I came across your library - thanks for putting this together! :construction_worker: 

I tossed a few quick tests around it for you. After you merge this you should be able to activate the build on travis-ci and stick a nice little build badge in your README.

The only code change I had to make was to add an explicit require for the `sidekiq/ruby` dependency. The tests don't pass without it.

Let me know if there are any changes you'd like me to make to help get this merged - thanks!

 - install rspec
 - cook up a few simple tests
 - add a .travis.yml for Travis-CI
 - add an explicit require for the squash_ruby dependency (so the tests
   work)