update-alternatives doesn't support ruby on 14.04

The tl;dr is that in Ubuntu 14.04, update-alternatives doesn't actually support `ruby` anymore, so linking the correct binaries in place must be done "manually." We'll do this with the link resource. For more background, see this bug report:

* https://bugs.launchpad.net/ubuntu/+source/ruby2.0/+bug/1310292

And this gist:

* https://gist.github.com/jtimberman/1c9cfee514644a04f9c2