Increase line height for masthead h1s

The line-height was pretty tight for multi-line headers in our masthead on desktop/tablet. I opened it up a bit to so it doesn't look squished together.

Before:
![image](https://cloud.githubusercontent.com/assets/6456757/5211611/efff27b6-759a-11e4-8603-4fc5eca79157.png)

With changes:

![image](https://cloud.githubusercontent.com/assets/6456757/5211623/2211478e-759b-11e4-8965-17fea328cc39.png)