Move postcss to peerDependencies

[ilfa]

It will be great not to download extra version of postcss.

More details you can find in this article https://nodejs.org/en/blog/npm/peer-dependencies/.

I can create a PR if you are ok.

[MadLittleMods]

@ilfa Is this the proper way to handle this nowadays? Any docs for PostCSS specifically?

Looking through a bunch of popular PostCSS plugins, they aren't doing this:

• https://github.com/pascalduez/postcss-apply/blob/70d8c6284e1c96659283f38ebd236002de144f1c/package.json#L44
• https://github.com/stylelint/stylelint/blob/97eb96d71e5c46596cd3c840aced377fc6888e1a/package.json#L139
• https://github.com/ismamz/postcss-utilities/blob/4be3c7dee84fd4634c4e8a12e13737ea451cd472/package.json#L26

I do see that Autoprefixer does this:

• https://github.com/postcss/autoprefixer/blob/abe667cc847dae09e30bfec746652d4a4b8daa39/package.json#L29

[ScottAwesome]

@MadLittleMods since the move to postcss 8, in the Plugin BoilerPlate Repo they are showing postcss as a peerDependency.

edit: I found the migration guide, and it is now an official recommendation:

Official Migration Guide

[MadLittleMods]

Thanks for the context @ScottAwesome!

@ilfa Feel free to create a PR 👍

[MadLittleMods]

Fixed in #129 and shipped in postcss-css-variables@0.18.0 🚀

Thanks to @delucis for the contribution ❤️