Fixed margins in nav bar on mobile

Removed the margin-bottom rule from:

.nav-justified>li>a of the /assets/application-25b8d7709fc3c19033d1292decf2d537.css:3892 (line 3892)

to remove the empty space at mobile resolutions.

[Before](http://i.imgur.com/2egBnON.png)
[After](http://i.imgur.com/YHL4TV8.png)
Merge pull request #26 from danbartram/patch-1

Fixed margins in nav bar on mobile