Fix API documentation font-family

Before:

![screenshot from 2014-01-17 14 42 00](https://f.cloud.github.com/assets/153842/1940679/46143f48-7f7d-11e3-9824-c6596ac64215.png)

After:

![screenshot from 2014-01-17 14 42 22](https://f.cloud.github.com/assets/153842/1940680/49d7fff2-7f7d-11e3-976a-73069d881a39.png)