repo.owner isn't working

It expands into a null string, I have to change it to `repo.namespace` mentioned in [Variables | Drone](https://docs.drone.io/template/variables/#repo) to work.

Start with the linked Drone Variables documentation, especially the repo.namespace entry, then locate this plugin’s template-variable expansion path. Confirm the intended behavior for repo.owner and repo.namespace, and verify that repo.owner no longer expands to a null string.

Written by the indexing model from the issue text.