Fix overflowing charts in firefox

![screen shot 2014-04-23 at 11 34 54 am](https://cloud.githubusercontent.com/assets/860492/2779610/b694ffa2-cafd-11e3-9281-1f9e309f77d2.png)

Small bug in the existing css in firefox where the charts would overflow the containers.

Double-checked chrome rendering after fix, should be fine in both browsers.