Add rbenv-ruby-2.1.1 package

Note: Starting with 2.1.0, ruby has switched to a versioning scheme that almost but not quite totally unlike semver[1].  Hence the package version doesn't have a patchlevel in it.

[1] https://www.ruby-lang.org/en/news/2013/12/21/semantic-versioning-after-2-1-0/