[BREAKING CHANGE] Upgrade ESLint to v6

[tetsuharuohzeki]

• https://eslint.org/blog/2019/06/eslint-v6.0.0-released
• https://eslint.org/docs/user-guide/migrating-to-6.0.0

TODO

• Check all migrating guides.
• Wait [parser] Error with ESLint 6.0.0 pre-releases typescript-eslint/typescript-eslint#563 coming to the release.
  • By Bump @typescript-eslint/eslint-plugin from 1.10.2 to 1.11.0 #129