Support ESLint v7

[koba04]

ESLint v7 has been released so we'd like to support ESLint v7.
https://eslint.org/blog/2020/05/eslint-v7.0.0-released

THIS PR IS A BREAKING CHANGE because this drops to support ESLint v6.

Tasks

• update ESLInt in devDeps and peerDeps
• use ESLint class instead of CLIEngine
• Update all plugins versions that are compatible ESLint v7
  • @typescript-eslint/eslint-plugin ESLint v7 typescript-eslint/typescript-eslint#1550
  • @typescript-eslint/parser ESLint v7 typescript-eslint/typescript-eslint#1550
  • eslint-plugin-jsx-a11y https://github.com/evcohen/eslint-plugin-jsx-a11y/issues/683
  • eslint-plugin-prettier Add tests for running ESLint 7 prettier/eslint-plugin-prettier#291
  • eslint-plugin-react [New] support eslint v7 jsx-eslint/eslint-plugin-react#2635
  • eslint-plugin-react-hooks feat(eslint-plugin-react-hooks): Support ESLint 7.x facebook/react#18878

[koba04]

You would see the warning while installing this config.

warning " > eslint-plugin-jsx-a11y@6.2.3" has incorrect peer dependency "eslint@^3 || ^4 || ^5 || ^6".

But eslint-plugin-jsx-a11y has supported ESLint v7 at the latest commit, which hasn't been published yet, and the commit has no changes for their source code, so we can update ESLint to v7 safely even though the waring.

jsx-eslint/eslint-plugin-jsx-a11y@b273fe5

[MRTAFU]

LGTM 🎉

[koba04]

Thank you!