Fold potentially noisy RVM fetching

Hide the following noise when using rubies that need fetching (such as 2.1.1, currently):

![travis ci - hosted continuous integration that just works 2014-05-02 23-21-34 2014-05-02 23-54-09](https://cloud.githubusercontent.com/assets/2560/2869787/bae76a74-d28f-11e3-9353-09bcc14829a6.png)