feat: upgrade postcss to 8.x
feat: upgrade postcss to 8.x

BREAKING CHANGE: upgrade postcss to 8.x

Co-authored-by: Edward Elric <c0170474dc6b058a718e1a8d3790775d9990182d@gmail.com>
Co-authored-by: Ward Peeters <f7d6f8166205aa91930091f422c0634df8a7ceb4@coding-tech.com>
egoist/rollup-plugin-postcss