PostCSS 8 support

[ai]

PostCSS 8.0 changelog

• [ ] Move postcss to peerDependencies
• [ ] Update install docs
• [ ] Update postcss version

[RyanZim]

Also:

• [ ] Update https://github.com/postcss/postcss-reporter version
• [ ] Upgrade or migrate away from https://github.com/michael-ciniawsky/postcss-load-config

[ai]

@RyanZim I updated postcss-load-config to support PostCSS 8 and released in 2.1.1.

Let’s use it to release PostCSS 8 support faster.

[RyanZim]

Yep, if postcss-load-config is up to date, I'm fine with using it.