Addresses part of #13643: Correct webkit-linear-gradient syntax in horizontal gradients

dist/css/bootstrap.css

@@ -5702,10 +5702,9 @@ button.close {
   opacity: .5;
 }
 .carousel-control.left {
-  background-image: -webkit-linear-gradient(left, color-stop(rgba(0, 0, 0, .5) 0%), color-stop(rgba(0, 0, 0, .0001) 100%));
+  background-image: -webkit-linear-gradient(left, rgba(0, 0, 0, .5) 0%, rgba(0, 0, 0, .0001) 100%);
   background-image:      -o-linear-gradient(left, rgba(0, 0, 0, .5) 0%, rgba(0, 0, 0, .0001) 100%);
   background-image: -webkit-gradient(linear, left top, right top, from(rgba(0, 0, 0, .5)), to(rgba(0, 0, 0, .0001)));
-  background-image: -webkit-linear-gradient(left, rgba(0, 0, 0, .5) 0%, rgba(0, 0, 0, .0001) 100%);
   background-image:         linear-gradient(to right, rgba(0, 0, 0, .5) 0%, rgba(0, 0, 0, .0001) 100%);
   filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#80000000', endColorstr='#00000000', GradientType=1);
   background-repeat: repeat-x;
@@ -5713,10 +5712,9 @@ button.close {
 .carousel-control.right {
   right: 0;
   left: auto;
-  background-image: -webkit-linear-gradient(left, color-stop(rgba(0, 0, 0, .0001) 0%), color-stop(rgba(0, 0, 0, .5) 100%));
+  background-image: -webkit-linear-gradient(left, rgba(0, 0, 0, .0001) 0%, rgba(0, 0, 0, .5) 100%);
   background-image:      -o-linear-gradient(left, rgba(0, 0, 0, .0001) 0%, rgba(0, 0, 0, .5) 100%);
   background-image: -webkit-gradient(linear, left top, right top, from(rgba(0, 0, 0, .0001)), to(rgba(0, 0, 0, .5)));
-  background-image: -webkit-linear-gradient(left, rgba(0, 0, 0, .0001) 0%, rgba(0, 0, 0, .5) 100%);
   background-image:         linear-gradient(to right, rgba(0, 0, 0, .0001) 0%, rgba(0, 0, 0, .5) 100%);
   filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#00000000', endColorstr='#80000000', GradientType=1);
   background-repeat: repeat-x;

less/mixins/gradients.less

@@ -7,7 +7,7 @@
   // Creates two color stops, start and end, by specifying a color and position for each color stop.
   // Color stops are not available in IE9 and below.
   .horizontal(@start-color: #555; @end-color: #333; @start-percent: 0%; @end-percent: 100%) {
-    background-image: -webkit-linear-gradient(left, color-stop(@start-color @start-percent), color-stop(@end-color @end-percent)); // Safari 5.1-6, Chrome 10+
+    background-image: -webkit-linear-gradient(left, @start-color @start-percent, @end-color @end-percent); // Safari 5.1-6, Chrome 10+
     background-image: -o-linear-gradient(left, @start-color @start-percent, @end-color @end-percent); // Opera 12
     background-image: linear-gradient(to right, @start-color @start-percent, @end-color @end-percent); // Standard, IE10, Firefox 16+, Opera 12.10+, Safari 7+, Chrome 26+
     background-repeat: repeat-x;