Move to PostCSS version 6

[teleclimber]

Can we upgrade to PostCSS version 6? The package.json calls for ^5.0.10.

Some PostCSS plugins fail to run on 5.x and I suspect the situation is only going to get worse. If we stay on 5.x we will miss the improvements made to plugins.

For example when I use postcss-nested latest version (2.1.2) I get an error saying I need to use PostCSS 6. I'd have to use 1.x of that plugin with vuefiy, which is many versions behind: https://github.com/postcss/postcss-nested/blob/master/CHANGELOG.md

Thanks.

[jonty-comp]

This is now a problem for me, as I am using Vueify with postcss-cssnext and get an node.parent.after is not a function error. Is this project dead? :(