Yes I'm referring to the Dockerfile. I'm no expert with Docker either, but I must admit that it's extremely handy for creating forums on the fly with different versions at the same time, and saves a lot of time.
If you're not focused on this tool I completely understand and appreciate you already providing up-to-date docker images, so I'll try to see what I can do myself and share it if it works well. This is possible by manually modifying the dockerfile but I think it's also possible in a more elegant way and easy to use, with env variables 😉