Create official docker image

[simonszu]

It seems that currently there is no official docker image, just some images on docker hub created by other users - which is uncomfortable since either one has to rely on these images which can be quite old and not frequently updated, or one has to build their own image, which somehow defeats the purpose of docker.

It would be great if there would be an official geemusic image, maybe automatically created by github-docker-webhook-triggers or via Travis CI.

[mikeage]

If you build your own, I suggest you take PR #249 , to handle the fact that Alpine now includes a newer pip than what was available when the Dockerfile was first created.