Merge pull request phaserjs#2483 from zeterain/patch-6

Update Documentation in Game.js

Author: photonstorm

src/core/Game.js

@@ -122,7 +122,7 @@ Phaser.Game = function (width, height, renderer, parent, state, transparent, ant
     this.renderer = null;
 
     /**
-    * @property {number} renderType - The Renderer this game will use. Either Phaser.AUTO, Phaser.CANVAS or Phaser.WEBGL.
+    * @property {number} renderType - The Renderer this game will use. Either Phaser.AUTO, Phaser.CANVAS, Phaser.WEBGL, or Phaser.HEADLESS.
     * @readonly
     */
     this.renderType = Phaser.AUTO;