you are right, we should not use nightly here! Thanks for pointing that out. We actually have a tag latest, which always points to the latest officially released version of Ray (see the doc in Docker Hub). We use that in the non-k8s based autoscalers and should change the k8s operator to use that too. If a user wants to use a specific version of Ray I think it is reasonable to expect that they can set the tag to a fixed version.
We are not currently doing minor versions like 1.2.1.
As for the documentation, whether the docs should point to master or the latest release is an open question cc @rliaw You can always see the latest release by going to the link What is Ray? — Ray v1.2.0