Merge pull request phaserjs#3741 from TadejZupancic/patch-5

Zone inside a Container fix

Author: photonstorm

src/gameobjects/zone/Zone.js

@@ -256,6 +256,18 @@ var Zone = new Class({
         return this;
     },
 
+    /**
+     * A NOOP method so you can pass a Zone to a Container.
+     * Calling this method will do nothing. It is intentionally empty.
+     *
+     * @method Phaser.GameObjects.Zone#setAlpha
+     * @private
+     * @since 3.10.0
+     */
+    setAlpha: function ()
+    {
+    },
+    
     /**
      * A Zone does not render.
      *