Bugfix: Docker image tag with underscores

Context

The docker image was not being found if the branch name had underscores instead of hyphens, it was defaulting to develop. CI_COMMIT_REF_SLUG replaces everything except a-z or 0-9 with "-", so it was searching for the wrong image tag.

Summary

I updated the regex to replace underscores with hyphens in the branch name. This should cover everything because branch names should only contain "/", "-", or "_", no spaces or other characters.

How was this tested?

Tested the build and run (osx) scripts on a branch with underscores and it successfully found the correct image.