Merge pull request #4274 from Marmelatze/three-color-gradient

Force percentage value on .vertical-three-colors() gradient mixin.

less/mixins.less

@@ -432,7 +432,7 @@
     background-color: mix(@midColor, @endColor, 80%);
     background-image: -webkit-gradient(linear, 0 0, 0 100%, from(@startColor), color-stop(@colorStop, @midColor), to(@endColor));
     background-image: -webkit-linear-gradient(@startColor, @midColor @colorStop, @endColor);
-    background-image: -moz-linear-gradient(top, @startColor, @midColor @colorStop, @endColor);
+    background-image: -moz-linear-gradient(top, @startColor, @midColor @colorStop*100%, @endColor);
     background-image: -o-linear-gradient(@startColor, @midColor @colorStop, @endColor);
     background-image: linear-gradient(@startColor, @midColor @colorStop, @endColor);
     background-repeat: no-repeat;