Added Context2d#createLinearGradient()

lib/canvas.js

@@ -119,11 +119,14 @@ Canvas.prototype.getContext = function(contextId){
   }
 };
 
+Context2d.prototype.createLinearGradient = function(x0, y0, x1, y1){
+  return new CanvasGradient(x0, y0, x1, y1);
+};
+
 Context2d.prototype.createRadialGradient = function(x0, y0, r0, x1, y1, r1){
   return new CanvasGradient(x0, y0, r0, x1, y1, r1);
 };
 
-
 /**
  * Set the fill style with the given css color string.
  *