[deps] eslint@7, prettier@2 의 변경사항 및 호환성 점검

[boxersb]

• eslint 7 Migration guide
  • https://eslint.org/docs/user-guide/migrating-to-7.0.0#plugin-loading-change
• prettier 2.0
  • https://prettier.io/blog/2020/03/21/2.0.0.html

[boxersb]

typescript-eslint@3.0 Release note

• https://github.com/typescript-eslint/typescript-eslint/releases/tag/v3.0.0

[boxersb]

prettier/prettier#8318 (comment)

프리티어 없애버릴까...