Stop bolding numeric arguments

This makes numeric arguments look more like arguments.

Before/after:
![screen shot 2014-07-08 at 14 54 14](https://cloud.githubusercontent.com/assets/1578238/3515009/4f0ea684-06d1-11e4-9f7f-aa997bf85ebd.png) ![screen shot 2014-07-08 at 14 54 29](https://cloud.githubusercontent.com/assets/1578238/3515010/511c3716-06d1-11e4-87aa-363cac50d4eb.png)