Stop bolding numeric arguments

This makes numeric arguments look more like arguments.

Before/after:
![screen shot 2014-07-09 at 14 32 00](https://cloud.githubusercontent.com/assets/1578238/3529215/57a399fa-0797-11e4-9ee8-d8288b08dec4.png) ![screen shot 2014-07-08 at 14 54 29](https://cloud.githubusercontent.com/assets/1578238/3515010/511c3716-06d1-11e4-87aa-363cac50d4eb.png)

![comparison](https://cloud.githubusercontent.com/assets/1578238/3529267/f3090880-0797-11e4-85cd-7a757edfddbd.png)