Fix vertical alignment of #omnibar-defaultEngineName

Before:
![win7-orig](https://cloud.githubusercontent.com/assets/1687481/4252329/2ab59ed0-3a95-11e4-9e28-e71ff8c5939d.png)

After:
![win7](https://cloud.githubusercontent.com/assets/1687481/4252328/2aa100e2-3a95-11e4-910b-6e24cff89850.png)

// I have similar results on Windows XP and Linux too.