Badges are crisper as svg

SVG readme badges are crisper :)

Before:
![screen shot 2014-11-25 at 14 41 39](https://cloud.githubusercontent.com/assets/162976/5177713/e83b6b28-74b1-11e4-922b-31ecba093066.png)

After:
![screen shot 2014-11-25 at 14 47 11](https://cloud.githubusercontent.com/assets/162976/5177718/f714fa24-74b1-11e4-854b-07bba1f9d796.png)