v3.4.0
- [upgrade] @typescript-eslint 3.9.0
- [rule] add @typescript-eslint/no-extra-non-null-assertion
- [rule] add @typescript-eslint/no-unused-vars-experimental
- [rule] add @typescript-eslint/prefer-nullish-coalescing
- [rule] add @typescript-eslint/prefer-optional-chain
- [rule] add @typescript-eslint/return-await