Fix for ESLint version 6

Hi friends!

This release fixes an oversight when using ESLint version 6:

• bug #732 feat: add ESLint 6 support - thanks to @Kocal
• minor #733 build(deps-dev): update eslint-loader to ^3 thanks to @Kocal

To upgrade:

1. Update your package.json file: set the @symfony/webpack-encore version to ^0.29.1.

2. Run yarn upgrade!

Changes: v0.29.0..v0.29.1

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

Happy packing!