Use the latest docker version in alpine-based images.

When using alpine latest + Docker 18.09.8-ce, the "docker pull"
command sometimes fails with an error such as:

"failed to register layer: Error processing tar file(exit status 1): operation not permitted"

By updating Docker to version 19.03 the problem goes away, suggesting
that the cause is some incompatibility between the docker 18.09
and the alpine-based libraries.

Author: ctalledo