replaced babel-polyfill

What does this MR do?

replaces babel-polyfill, which got introduced in !877 (merged) by regenerator-runtime, as the prior was throwing warnings due to its use of the outdated core-js 2. We are now purely on core-js 3.

How confident are you it won't break things if deployed?

Should work.

Links to related issues

https://stackoverflow.com/questions/58919016/babel-and-webpack-are-throwing-cant-resolve-regenerator-runtime-runtime

https://babeljs.io/docs/en/babel-polyfill

https://stackoverflow.com/questions/57101261/webpack-package-babel-polyfill-has-been-deprecated-how-to-use-an-alternati

How to test

Use the beta page on many different browsers.

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings