Eliminate deprecation warnings in tests
Add multiple Rails versions to tests.  Restrict to Rails 3.1+ for MultiJson compatibility.  Add Ruby 2.0.0 to tests.  Allow testing against Rails 4.
Update .travis.yml with 2.1.0 and new Rubinius label.  Add Rubinius gems.
Merge pull request #43 from petergoldstein/feature/add_multiple_rails_versions_to_travis

Improve Travis tests