Use ruby 2.1.1
Specify 2.1 ruby in Travis

Now that ruby supports semantic versioning and ruby 2.1.1 is out,
Travis supports 2.1 as a valid version that will run the latest 2.1.x.

https://twitter.com/teeparham/status/438002030146117632
Merge pull request #750 from haml/ruby_2.1

Use ruby 2.1.1, specify 2.1 in travis