Use PostCSS async API

[ai]

css-loader uses sync API for PostCSS.

It is restricted by PostCSS Runner Guielines, because you can’t use sync API with async plugins.

/cc @markdalgleish

[ai]

For example, cssnano can start to use async plugin.

[isairz]

I setup my webpack config following example.
https://github.com/emmenko/redux-react-router-async-example

This example occurs same errer. I think this is a good test case for this issue.

[ai]

Seems like cssnext-loader also uses sync API

[MoOx]

FYI, I am responsible of the current shit postcss/postcss#412 (comment)

[sokra]

Thanks for the hint. We should use the async API...

[timdorr]

cssnano v3.0.0 is out and requires usage of the async API. So, this is now a reality 😉