Update css/font-awesome.css

Fix font smoothing (was too blurry in webkit)

The problem:
 
With browser default (-webkit-font-smoothing:subpixel-antialiased)
![Captura de pantalla 2013-01-08 a la s 13 09 22](https://f.cloud.github.com/assets/122741/50015/c866b07e-598c-11e2-98ec-ecabcb0507c7.png)


With the fix (-webkit-font-smoothing:antialiased)
![Captura de pantalla 2013-01-08 a la s 13 09 29](https://f.cloud.github.com/assets/122741/50019/2889fcfe-598d-11e2-979c-63569abb902e.png)