Added test and fix for ruby versioning bug

This ruby bug has been showing up a lot recently and the real fix is to change a user's bash profile, but automatically changing someone's bash profile from this script seems kind of wrong, so just told them what to change if something's wrong. Tested on my local machine, if the user has no rvm then there should be a sensible error spit out, and I believe that would be caught earlier around line 300 so I didn't bother testing for it here. Let me know if you think it makes sense to test for that here as well.

@jkarni @jtauber