docs: readme: add 2021 and 2022 to supported ECMAScript versions

[coderaiser]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[x] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Updated list of supported ECMAScript versions according to https://eslint.org/blog/2021/08/eslint-v8.0.0-beta.0-released

Is there anything you'd like reviewers to focus on?

[eslint-github-bot]

Hi @coderaiser!, thanks for the Pull Request

The first commit message isn't properly formatted. We ask that you update the message to match this format, as we use it to generate changelogs and automate releases.

• The commit message tag must be one of the following:

  The Tag is one of the following:

  • Fix - for a bug fix.
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  • Breaking - for a backwards-incompatible enhancement or feature.
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  • Build - changes to build process only.
  • Upgrade - for a dependency upgrade.
  • Chore - for anything that isn't user-facing (for example, refactoring, adding tests, etc.).

  You can use the labels of the issue you are working on to determine the best tag.

• There should be a space following the initial tag and colon, for example 'New: Message'.

• The first letter of the tag should be in uppercase

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