Allow less-loader 10 and postcss-loader 6

Hi Webpackers!

This release allows the latest less-loader and postcss-loader to be used:

Feature

• #1008 - Allow postcss-loader 6 - @bobvandevijver
• #1009 - Allow less-loader 10 - @bobvandevijver

To upgrade run:

yarn upgrade "@symfony/webpack-encore@^1.6.0"

Changes: v1.5.0..v1.6.0

Documentation: http://symfony.com/doc/current/frontend.html

Happy packing!