Update to PostCSS 8

[onigoetz]

Hello,

This PR makes the following changes, fixes #20

• Update this module to PostCSS 8 using the migration guide : https://evilmartians.com/chronicles/postcss-8-plugin-migration
• Update the node version to use 10 at the minimum
• Remove the babel build step
• Replace Jest with Mocha (way less dependencies to install, the advanced features of Jest aren't needed here)
• Update TypeScript Typings
• Add GitHub Actions

[Knagis]

FYI: https://www.npmjs.com/package/@notiv/postcss-property-lookup an existing fork of this plugin with PostCSS8 support.

[simonsmith]

@onigoetz Changes look good. Will merge and release when I get a free moment. Appreciate it

[simonsmith]

Only change I'd recommend is using yarn and removing the package-lock.json.

[onigoetz]

Sure can do, I also prefer Yarn I just didn't want to introduce more changes than needed :)

[onigoetz]

Oh, I missed that the yarn.lock already existed.
Change done

[simonsmith]

It looks like yarn.lock has been deleted in the diff?

[onigoetz]

Yes it looks like it but actually it's just 2'000 lines shorter. if you load the diff you'll see there is still content.
The main reason is the removal of Babel and Jest.

[simonsmith]

Ah sorry, of course. My bad!

[simonsmith]

Done - https://github.com/simonsmith/postcss-property-lookup/releases/tag/3.0.0

Thanks @onigoetz