Fix Gemfile, Fix tests, turn unshorten into a module, Fix bug with weird chars in original url

Hi there, thanks for writing this gem.

I've went through and fixed a few problems I've had with it on ruby 2.1.2 and a modern version of rake:

 - I added the rubygems source to the gemfile
 - I got the tests passing again by replacing "uri.path.present?" with uri.path which does what was intended
 - I fixed another test which was checking for the wrong url
 - I added another test for a URL I found which was breaking unshorten
 - I incremented the version number and moved it into a separate file
 - I made Unshorten a module instead of a class

Thanks
JH