Fix for clearing thumbs layout #2068

Bug demonstrated here:
http://lukebussey.com/foundation-clearing-bug/

Fix demonstrated here:
http://lukebussey.com/foundation-clearing-fix/
Updating _clearing.scss styles to match that of docs.scss and removed code from docs.scss
Merge pull request #2204 from lukebussey/clearing-layout-fix

Fix for clearing thumbs layout #2068