Overflow issue on .sr-only

Created by: Lausselloic

As identified by @Orhleil on boosted : https://github.com/Orange-OpenSource/Orange-Boosted-Bootstrap/issues/84

Reduced test case https://jsfiddle.net/etr3yjv6/10/

On chrome (v64 tested) there's an oveflow onto the main container. That one could be fixed by adding a margin: -1px onto the sr-only class