Fix for structure CSS minificator like cleancss

'promo-button' generated this code
{
	background-color: #000
	background: linear-gradient(...)
}

cleancss removes 'background-color' in favour more complex 'background'
Up dep, trying to handle travis 0.8 node problem
Merge branch 'cleancss-fix'

* cleancss-fix:
  Fix for structure CSS minificator like cleancss
v0.27.3