chore: update recommended config to @babel/eslint-parser

[Brianzchen]

Closes #474

Recommended config now uses @babel/eslint-parser. This should be a breaking change for consumers, the only difference should be that eslint how uses a projects babel config to read files which may cause issues if the babel config has exclusions setup based on environment variables that don't play nice with eslint.

This should be a major version bump.

@wilt-rally @gajus

[Brianzchen]

@gajus thoughts on this?

[gajus]

• What's the reason babel-eslint is kept as a dependency?
• What's the reason @babel/eslint-parser is not a dependency?

[Brianzchen]

• What's the reason babel-eslint is kept as a dependency?

babel-eslint is a dev-dependency of this project is because the eslint rules of this project don't use itself, the dependency here also isn't what is shipped as a requirement to the user.

• What's the reason @babel/eslint-parser is not a dependency?

This project doesn't use @babel/eslint-parser again because of the eslint rules it extends from are not itself. The current version of canonical eslint still uses babel-eslint https://github.com/gajus/eslint-config-canonical/blob/v20.1.0/configurations/eslintrc.json#L7. We can upgrade this as part of a separate PR because updating the dev dependencies here is not really the goal of this PR

---

Overall what i'm trying to do here is just update what is used by the consumer so that they get @babel/eslint-parser out of the box without needing to override babel-eslint not what this project (eslint-plugin-flowtype) internally uses.