big thread about it here Broken shadows after recent Chrome update in 4.2 - #37 by nima
. they already published a 4.2.1 to the babylon cdn. You can also access it in your app using the github cdn by importing from babylonjs.github.io/cdn/babylon.js
you could also copy/paste CDN/babylon.js at master · BabylonJS/CDN · GitHub into your app and manually redeploy