Fixes issue where modal heading could overlap button.

![screen shot 2014-05-20 at 9 46 30 am](https://cloud.githubusercontent.com/assets/583202/3027770/e8974f0e-e025-11e3-98ef-325f4cc8729f.png)

Fixes DoSomething/dosomething#2217.
For review: @DoSomething/front-end