navbar form-group in mobile adds extra margin

Created by: fletch3555

Having a .form-group within a .navbar-form produces a margin-bottom: 5px in the xs view. This is obviously to add spacing between adjacent .form-groups, but the spacing looks weird when there's only one element there.

In this fiddle(http://jsfiddle.net/29ywdc1x/1/), I've added some CSS to zero the margin if the .form-group is the :last-child of it's parent. The fiddle uses the 3.2.0 release from bootstrapcdn, but I discovered it while working locally right after syncing with master.

Let me know what you guys think.