Mobile button fix.

As on mobile we are using Helvetica font this is happening:
![screen shot 2014-10-16 at 12 28 17](https://cloud.githubusercontent.com/assets/2579465/4662572/17d5f6bc-5533-11e4-959c-a6e63b62080e.png)

So for lower resolutions I am adding different line height.
![screen shot 2014-10-16 at 12 28 29](https://cloud.githubusercontent.com/assets/2579465/4662580/288b039e-5533-11e4-8b73-dbfb40482282.png)

Downside is that it won't work when playing with window size on desktop + possibly some mobile devices when changing from portrait to landscape etc.