BREAKING CHANGE: Enable several rules related to ES6 features, mostly
promises and async/await but a few other features as well.
One rule, 'require-atomic-updates', was introduced in ESLint 5.3.0 so
that's now the minimum specified in peerDependencies.
https://github.com/tc39/proposal-object-rest-spread has become a part
of the ECMAScript standard as of version 2018 (also known as ECMAScript
9).
experimentalObjectRestSpread will be removed in the future from eslint.
