If you get this error:
$ docker-compose build db uses an image, skipping Building heroku ERROR: Couldn't connect to Docker daemon - you might need to run `docker-machine start default`.
And Docker logs something like:
Nov 11 13:13:45 ultra0 dockerd: time="2017-11-11T13:13:45.000484088-03:00" level=error msg="Handler for POST /v1.22/build returned error: Error processing tar file(archive/tar: invalid tar header): "
It means there is at least one file in your project it is owned by root.
To fix it just
chown all your files to yourself:
$ sudo chown -R USERNAME.USERNAME /path/to/project
Or if you are on your project:
$ sudo chown -R $(whoami).$(whoami) .