This increases supported browser versions to:

- Google Chrome/Chromium: at least major version 84 because older
  versions have an annoying bug with Array.reduce:
  https://bugs.chromium.org/p/chromium/issues/detail?id=1049982
- Microsoft Edge: at least majoy version 84 (dropping support for
  pre-Chromium Edge). (Same reasoning as with Chrome)
- Mozilla Firefox: at least major version 78, as this is the latest ESR
  and it is used quite a lot.
- Apple Safari: at least major version 13 (dropping support for
  Safari 12) because it is the second latest version of Safari

Changelog: changed