Change the default policy to pull a versioned image from docker hub

[animeshsingh]

use a tagged image, like ":master-36" - that tagging should be part of ci/cd

[fplk]

We think this is closed in #79 but I cannot close the issue myself, since I'm not listed as a contributor to this project. Also cmp. #28

[Tomcli]

Closed in #79