We used the image of 7.1 from docker hub, switched edition to develop (this has installed license plugin) and it is working since then. For the version 7.5 we are going to create our own image. We have just started to create docker file. All I can offer you right now is this comment. I cannot guarantee that is will work in any way. I hope that when we find a working solution for dev edition of 7.5 then we will open the source on github.