Updated existing for TS defs. Fix phaserjs#4941

Author: photonstorm

CHANGELOG.md

@@ -164,7 +164,7 @@
 
 My thanks to the following for helping with the Phaser 3 Examples, Docs and TypeScript definitions, either by reporting errors, fixing them or helping author the docs:
 
-@fselcukcan Bambosh @louisth @hexus @javigaralva @samme @BeLi4L @jcyuan @javigaralva 
+@fselcukcan Bambosh @louisth @hexus @javigaralva @samme @BeLi4L @jcyuan @javigaralva @T-Grave
 
 
 ## Version 3.21.0 - Senku - 22nd November 2019

src/gameobjects/GameObjectFactory.js

@@ -112,7 +112,7 @@ var GameObjectFactory = new Class({
      * @method Phaser.GameObjects.GameObjectFactory#existing
      * @since 3.0.0
      *
-     * @param {Phaser.GameObjects.GameObject} child - The child to be added to this Scene.
+     * @param {(Phaser.GameObjects.GameObject|Phaser.GameObjects.Group)} child - The child to be added to this Scene.
      *
      * @return {Phaser.GameObjects.GameObject} The Game Object that was added.
      */