Adjust size of Bitcoin address on small screens

Fixes #2150. Prevents a horizontal scrollbar from appearing viewing profiles with Bitcoin addresses (mostly on iPhones). I decreased the size instead of trying to cut it off with an ellipsis because the implementation is a lot easier and some people may reference addresses by the last few digits.

![screen shot 2014-03-16 at 7 10 27 pm](https://f.cloud.github.com/assets/65468/2432331/2d7eee5e-ad60-11e3-8e3d-585592c28939.png)