example repo fails with 404; turn backslash into slashes to fix it

[godmar]

The example repo, when cloned into the server folder of nginx, fails to work via localhost on Ubuntu/Linux. For instance, going to http://localhost/phaser3-examples/public/boot.html?src=src\camera\multi%20camera\boot.json attempts to access http://localhost/phaser3-examples/public/Controller.js?=1597765543353 instead of http://localhost/phaser3-examples/public/src/camera/multi%20camera/Controller.js?=1597765624222 resulting in a 404.

This patch fixes the provided repo when served directly in this way. The code in index.html appears to use slashes. Tested on Linux/nginx/Firefox via localhost (not tested on Windows). I do not know what strategy for converting slashes/backslashes is being used.