Use eslint --report-unused-disable-directives in react-scripts fork

[frank-west-iii]

As of eslint 4.8.0, there is a new --report-unused-disable-directives option that will report if it finds any eslint-disable comments that are no longer relevant.

We should add this to our react-scripts fork.

Referenced from here: CodingZeal/generator-react-zeal#85