When using the old webpack-dev-server with webpack 5+, we get bitten
by webpack/webpack-dev-server#2692. This upgrades to 4.0.0-beta1 which
also (unhelpfully) changes the config options. The `watchContentBase`
and `watchOptions` don't seem to have analogs in the new versions, but
I left them commented out for future reference.
Also, this does not update `package-lock.json` because even just
updating locally gave different output since I'm on a different
version of node, I'm guessing.