Small fix - updated library

Hello, tiny update today for City Catformer!

It hasn't been working for a while, it seems that BabylonJS have incorporated the previewing mesh loader extension into an official extension, and the old library stopped working. So I just changed to a new official library and it works again!

BabylonJS was lots of fun to work with, I'd like to make another BabylonJS game again one day, or work on this one.

Game works best in fullscreen.