Add width to search input box

This adds a width to the input box, which makes the menu a little better looking when there is a very long site name in the drop down menu. 

Before: 
![screen shot 2014-08-21 at 1 47 52 pm](https://cloud.githubusercontent.com/assets/1452285/4000645/b8e08b8e-295b-11e4-90ff-5d355a6b146e.png)

After: 
![screen shot 2014-08-21 at 1 46 57 pm](https://cloud.githubusercontent.com/assets/1452285/4000647/c131507a-295b-11e4-86b3-a7a9de9957aa.png)