Running webpacker:install adds webpack-dev-server ^4.0.0 and the configuration has changed.

[coder2000]

When running webpacker:install as described in the upgrade steps it replaces webpack-dev-server 3.11.2 with 4.0.0, which is good, however it also causes issues as the configuration options have changed for dev-server.

https://github.com/webpack/webpack-dev-server/blob/master/migration-v4.md

[anark]

See #3122 and #2994

[dhh]

Closed by #3122.