[TASK] Use the latest Ruby 2.1 release for Travis.

Starting with Ruby 2.1, Ruby uses Semantic Versioning. Selecting
version "2.1" in the Travis configuration means that the latest
2.1 patch release will be used.

https://github.com/travis-ci/travis-ci/issues/2220#issuecomment-42263699
Merge pull request #3 from braingourmets/task/ruby-version

[TASK] Use the latest Ruby 2.1 release for Travis.