This PR downgrades the docker dependency to the stable 19.03 branch.
It means that we will negociate 1.40 by default and not the uncomplete
1.41 API.
It was not possible to use the stable branch before because a patch
was pending to build on netbsd and dragonfly:
a40b877fbb
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
Julien Pivotto
jojohappy
Fabian Reinartz