added getter for center of mass

Author: CodeAndWeb

src/physics/matter-js/components/Mass.js

@@ -5,6 +5,7 @@
  */
 
 var Body = require('../lib/body/Body');
+var Vector2 = require('../../../math/Vector2');
 
 /**
  * [description]
@@ -46,6 +47,14 @@ var Mass = {
         Body.setDensity(this.body, value);
 
         return this;
+    },
+
+    centerOfMass: {
+
+        get: function ()
+        {
+            return new Vector2(this.body.render.sprite.xOffset * this.width, this.body.render.sprite.yOffset * this.height);
+        }
     }
 
 };