added support for postcss v8

[oscarotero]

Fixes #427
Supersedes #428

I did this changes following the plugin migration guide (https://evilmartians.com/chronicles/postcss-8-plugin-migration). I hope it helps.

[oscarotero]

I'm having the same CI errors than the previous PR. These errors are related with the source-map generation in windows (it seems like is about the directory separation).

[RyanZim]

@oscarotero Looks like it's just a paths issue, there's an HTML file in test/sourcemap to actually test the sourcemaps in your browser devtools; if the sourcemap is working fine, you can just update the expected result in the tests to get them passing.

[oscarotero]

I had to create a different sourcemap for windows to pass the tests, but it's working.

[RyanZim]

@oscarotero Were you able to verify that the sourcemap generated on Windows works correctly on Windows? If not, that's fine, just curious.

[oscarotero]

@RyanZim No, I don't have any Windows machine to verify that 😅

[bytestream]

@RyanZim Anything I can help with to get this merged?

[RyanZim]

Merged, need to do some other dependency upgrades before I release, but hopefully should be out this week.

[RyanZim]

Sorry so long, finally released in v13 yesterday 🎉

[bytestream]

Thanks man 🙌