Fix invalid options passed to dev-server

Hi Webpackers!

This release fixes a bug related to version 4 of webpack-dev-server (which is included in version 1 of this library). The code still relied on several, removed options. See #899 for more details.

yarn upgrade "@symfony/webpack-encore@^1.0.1"

Changes: v1.0.0..v1.0.1

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

Happy packing!