remove border around gravatars

There is this nearly invisible border around gravatar images. wouldn't it be better to remove it?

Have a look at github's gravatar:
![selection_124](https://f.cloud.github.com/assets/206108/2526918/fcf2a23e-b4fe-11e3-8b11-27b7a9b38aec.png)

Without the border the gravatar looks much nicer:
![selection_123](https://f.cloud.github.com/assets/206108/2526921/074bdcbe-b4ff-11e3-9efb-6fa762a77531.png)