Fix rule conflicts between ESLint and Prettier 2

[arianacosta]

yarn code:check:rules
yarn run v1.19.1
$ eslint --print-config .eslintrc.js | eslint-config-prettier-check
The following rules are unnecessary or might conflict with Prettier:

- arrow-parens

The following rules are enabled but cannot be automatically checked. See:
https://github.com/prettier/eslint-config-prettier#special-rules

- no-unexpected-multiline
- quotes