Docker image with dev tag should build from release branch

[breezykermo]

Currently the image on Dockerhub is only updated with commits on master. However, we're almost always working from the release branch, so this should probably build and push to Dockerhub as well.

Or, at the very least, the image that is built from master should no longer have the :dev tag.

[breezykermo]

This has now changed with our protocol switch to main/develop branches. The build still seems to be broken however, so I'll look into it.