Allow less-loader 9 & fix pesky bug with build cache

Hi Webpackers!

This release contains a bug fix if you're using Encore.enableBuildCache() and allows less-loader version 9. Thanks to @bobvandevijver for both of these - especially the bug fix, which was super tricky.

• [FEATURE] Allow less-loader v9 - #983 thanks to @bobvandevijver
• [BUG] Fix manifest key problem when using copy files - #936 thanks to @bobvandevijver

To upgrade run:

yarn upgrade "@symfony/webpack-encore@^1.4.0"

Changes: v1.3.0..v1.4.0

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

Happy packing!