Unpkg down again

Web server is returning an unknown error 
Error code 520

https://github.com/mjackson/unpkg/issues/389#issuecomment-2051679841

> Consider switching to a production focused CDN https://cdn.jsdelivr.net/npm/react@16.7.0/umd/react.production.min.js
>
> Tool for easy conversion https://www.jsdelivr.com/unpkg