fix extra margin in header css

This fixes the header -- it was annoying me that it was vertically off-center because of the input box.

before:
![screenshot from 2014-06-20 12 35 57](https://cloud.githubusercontent.com/assets/59292/3344775/5122e244-f8af-11e3-90b9-11a2a55639e2.png)

after:
![screenshot from 2014-06-20 12 36 09](https://cloud.githubusercontent.com/assets/59292/3344777/55e6174c-f8af-11e3-9172-08360426a407.png)