Support Ruby 2.2.0
Use new travis build infrastracture

The Travis CI Blog: Faster Builds with Container-Based Infrastructure and Docker
http://blog.travis-ci.com/2014-12-17-faster-builds-with-container-based-infrastructure/
Cancel new fature. `sudo` command in `before_script`
it does not works.
Merge pull request #33 from Tomohiro/ruby2.2.0