Use :ok status instead of :success

To receive 200 response code `Rack::Utils.status_code` should
receive `:ok` as argument value instead of `:success`.

http://rubydoc.info/github/rack/rack/Rack/Utils
Display deprecation warning for :success status
Merge pull request #89 from ck3g/change_success_status_to_ok

Change success status to ok