Fix the docker build to stop using Apache

[domenic]

If you use the --docker parameter to HTML build, it will build inside a Docker container then host the site using Apache. That will break after #139 and associated other PRs.

We should probably change it to use nginx, possibly with some copy of the config in misc-server.

This logic currently lives in https://github.com/whatwg/html-build/blob/master/Dockerfile. I use it every day as it's faster than using the web service and Wattsi doesn't work on Windows.