Always lint with latest React version

[Timer]

This is the best behavior so people have seamless upgrades to new React majors.

This is probably a terrible default warning from the ESLint plugin, and we need to wait for jsx-eslint/eslint-plugin-react#1955 before changing this hardcoded behavior.

Closes #5034

[gaearon]

lol ok

[Timer]

The old behavior was to lint against latest, we could talk about matching it to the package.json version but then people won't get warnings about unsafe lifecycles, so I think latest is good.

Without this patch console output was ugly:

joes-mbp:website joe$ yarn build
yarn run v1.9.4
$ react-app-rewired build
Creating an optimized production build...
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Warning: React version not specified in eslint-plugin-react settings. See https://github.com/yannickcr/eslint-plugin-react#configuration.
Compiled with warnings.

edit: they don't support latest so 999.999.999 is the next best thing because why not