grayscale for all

this mixin work in ie explorer too

@mixin grayscale  
  filter: url("data:image/svg+xml;utf8, <svg xmlns=\'http://www.w3.org/2000/svg\'> <filter id=\'grayscale\'> <feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/> </filter></svg>#grayscale")
  filter: gray
  -webkit-filter: grayscale(100%)