Minor tweak to badges in .btn-xs buttons

Make `.badge`'s fit and look better when used inside `.btn-xs` buttons.

Before:

![screenshot - 14-01-13 - 01 27 52 pm](https://f.cloud.github.com/assets/47756/1905121/33aff17a-7c9a-11e3-9f2d-9f4c9e1c8a40.png)

After:

![screenshot - 14-01-13 - 01 28 02 pm](https://f.cloud.github.com/assets/47756/1905123/3985a180-7c9a-11e3-9a8b-8994d274e1fb.png)