fix: Derive espree.Syntax from espree.VisitorKeys

[codeworrior]

Fixes #531.

If removing the lib/ast-node-types.js is regarded as an incompatible change, I can restore it and leave the cleanup up to you in one of the upcoming major releases. My assumption was that the module is rather an internal thing and not part of your APIs.

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Frank Weigel (6ea491e, a3e88ae)

[eslint-github-bot]

Hi @codeworrior!, thanks for the Pull Request

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[codeworrior]

Sorry for not immediately signing the CLA. I have to clarify with my employer first.

[nzakas]

LGTM. Just want another set of eyes before merging.

[mdjermanovic]

LGTM, thanks!

Waiting for CLA before merging.

[codeworrior]

Sorry for the delay. After my employer decided to sign the corporate CLA, we struggled a bit with the process and tooling, but now we're done.

[mdjermanovic]

Thanks for contributing!