Updated MRI ruby 2.1.5 -> 2.2.0

For more about this ruby version read:

	https://www.ruby-lang.org/en/news/2014/12/25/ruby-2-2-0-released/

No code changes needed, mostly garbage collection improvements.
Update ruby version to 2.2.0 in Gemfile. Ooops.
Updated eventmachine gem 1.0.3 -> 1.0.4

The old version didn't compile under ruby 2.2.0, which blocked the ruby upgrade.