Bump eslint from 4.18.2 to 6.6.0

Bumps [eslint](https://github.com/eslint/eslint) from 4.18.2 to 6.6.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/master/CHANGELOG.md)
- [Commits](eslint/eslint@v4.18.2...v6.6.0)

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Author: dependabot[bot]