Potential enhancement for line-clamp

[mob8607]

As we can use lh as height value, we can probably improve the line-clamp mixin.

Needs to be tested in all browsers.

@mixin line-clamp($clamp) {
  display: -webkit-box;
  -webkit-box-orient: vertical;
  -webkit-line-clamp: $clamp;
  max-height: #{$clamp}lh;
  overflow: hidden;
}