You cannot rename a file from webp to jpg, but you can change the URL to .jpg and it will likely serve you the jpeg version. You can also convert webp to another format with dwebp or MS Paint.

Oh, more meetings will fix it! /s

I would recommend making a full git repository and at least adding a license header so that others can expand upon it. Maintaining a useful gist is cumbersome as issues tend to be ignored comments.