Make getHoverColor() return the original value if it is CanvasGradient

Author: nagix

src/core/core.helpers.js

@@ -647,7 +647,7 @@ module.exports = function() {
 
 	helpers.getHoverColor = function(colorValue) {
 		/* global CanvasPattern */
-		return (colorValue instanceof CanvasPattern) ?
+		return (colorValue instanceof CanvasPattern || colorValue instanceof CanvasGradient) ?
 			colorValue :
 			helpers.color(colorValue).saturate(0.5).darken(0.1).rgbString();
 	};