Gate#make_shortenURL is moved to URLShortener
URLShortener is just a functor.
Merge branch 'master' of https://github.com/DonutWorks/Ari into refact/url-shortener-to-lib

Conflicts:
	app/models/gate.rb
	spec/models/gate_spec.rb
Merge pull request #98 from DonutWorks/refactor/url-shortener-to-lib

Gate#make_shortenURL is moved to URLShortener