Update postcss dependencies, drop EOL nodes

[pustovalov]

closes: #2745

https://github.com/webpack-contrib/postcss-loader/blob/master/CHANGELOG.md

the config option doesn't support Object type anymore, config.path and config.ctx options were removed

https://github.com/postcss/postcss-safe-parser/blob/master/CHANGELOG.md
https://github.com/postcss/postcss/blob/master/CHANGELOG.md

https://nodejs.org/en/about/releases/

Node: 11, 13, no longer supported and not receiving security update

[gauravtiwari]

Thanks @pustovalov Could you please rebase and I will merge, thank you.

[pustovalov]

@gauravtiwari done