Automate container push with Travis

[gsganden]

Right now I have to push new versions of the app to Dockerhub manually. Pushing them automatically as part of Travis builds when merging into master would be more reliable.

[davidwilby]

Happy to take a look at this (and maybe #110 too) if you still want help on this?

Couple of questions:

• would you prefer travis over github actions? (admittedly I think github actions has emerged since this issue was created)
• Where are the build instructions for the container? Is there an uncommitted Dockerfile somewhere?

[gsganden]

Great!

I would love to move to GitHub Actions.

The Dockerfile is in https://github.com/uptake/autofocus/blob/master/autofocus/predict/Dockerfile. It is specific to the app that serves predictions from a trained model.