Support for negative from angle

.background-image(linear-gradient(-135deg, #d63f3e 0%,#9f1897 100%));

resulted in
 
  background-image: -webkit-linear-gradient(--45deg, #d63f3e 0%, #9f1897 100%);
  background-image: -moz-linear-gradient(--45deg, #d63f3e 0%, #9f1897 100%);
  background-image: -o-linear-gradient(--45deg, #d63f3e 0%, #9f1897 100%);
  background-image: linear-gradient(-135deg, #d63f3e 0%, #9f1897 100%);