Integrating Cocosx JS 3.8 with Google Gameplay Services

cocos2d-x JavaScript
1

I am trying to integrate my game with Google Gameplay Services.

I am following this Tutorial @ http://blog.rhesoft.com/2015/04/20/tutorial-google-play-game-services-with-cocos2d-js-and-android/

I followed all steps and I call

jsb.reflection.callStaticMethod("org/cocos2dx/javascript/AppActivity", "showLeaderboards", "()V"); in the constructor of HelloWorldLayer.

and I get this error:
D/CCJavascriptJavaBridge(11630): Failed to find method id of org/cocos2dx/javascript/AppActivity.showLeaderboards ()V

Also copied the AppActivity from the provided GIST, which has showLeaderboard() function defined!

What could be the issue? Help please.