Switches dev versioning from being based on a set version like
`18.06.0-dev` to being based purely on the git commit timestamp / git
commit sha.
This should give us a bit more flexibility in terms of nightlies not
being tied to specific versions.
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>
Upstream-commit: 559c9a323a77fe1215f91d851ce72053ce5dd99b
Component: packaging