correct radial gradient format to w3c spec

Author: lukeapage

lib/less/functions.js

@@ -528,13 +528,14 @@ tree.functions = {
             case "to top right":
                 gradientDirectionSvg = 'x1="0%" y1="100%" x2="100%" y2="0%"';
                 break;
-            case "radial":
+            case "ellipse":
+            case "ellipse at center":
                 gradientType = "radial";
                 gradientDirectionSvg = 'cx="50%" cy="50%" r="75%"';
                 rectangleDimension = 'x="-50" y="-50" width="101" height="101"';
                 break
             default:
-                throw { type: "Argument", message: "svg-gradient direction must be 'to bottom', 'to right', 'to bottom right', 'to top right' or 'radial'" };
+                throw { type: "Argument", message: "svg-gradient direction must be 'to bottom', 'to right', 'to bottom right', 'to top right' or 'ellipse at center'" };
         }
         returner = '<?xml version="1.0" ?>' +
             '<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="100%" height="100%" viewBox="0 0 1 1" preserveAspectRatio="none">' +

test/less/errors/svg-gradient1.txt

@@ -1,4 +1,4 @@
-ArgumentError: error evaluating function `svg-gradient`: svg-gradient direction must be 'to bottom', 'to right', 'to bottom right', 'to top right' or 'radial' in {path}svg-gradient1.less on line 2, column 6:
+ArgumentError: error evaluating function `svg-gradient`: svg-gradient direction must be 'to bottom', 'to right', 'to bottom right', 'to top right' or 'ellipse at center' in {path}svg-gradient1.less on line 2, column 6:
 1 .a {
 2   a: svg-gradient(horizontal, black, white);
 3 }