Fixed the CSS on the sign up form for campaign updates

Hi, I was looking the website on Firefox, and the campaign update form was looking odd.
I've fixed it, and it's better now :)
![screenshot 2014-03-20 22 17 20](https://f.cloud.github.com/assets/4429/2479398/9e982004-b096-11e3-8bb2-9f7573ea9297.png)