Get polyfill.js from cloudflare

[fuggla]

Summary

Polyfill.io doesn't have the best reputation these days. I've changed the source of the script to cloudflare.

• https://blog.cloudflare.com/polyfill-io-now-available-on-cdnjs-reduce-your-supply-chain-risk
• https://blog.cloudflare.com/automatically-replacing-polyfill-io-links-with-cloudflares-mirror-for-a-safer-internet

Tests

The only test I've done is starting a container with LOCAL_MODE true and false. Can do additional tests but I'll need some pointers :)

Checks

• [X] Tested changes

[Linbreux]

@fuggla

This is indeed a better way. Thanks, LGTM!