After installing a new gem and trying to use it I noticed that all my gems were not working. They were still all installed because when I run 'gem list' a full list of installed gems were returned. After a lot of research on this I found I just had to run one command.
What this does is creates the 'shim' binaries required to make the correct version of Ruby available on the path at all times. So just to be safe make your to rehash after installing gems.