Enhancement request: support for tags on docker hub

[dutchiechris]

Request: Can the images pushed to publysher/hugo be tagged with the hugo release?

Reason: I use gitlab CI and the publysher/hugo container image to update my website after every push. Sometimes my hugo is out of date locally, so my local test works fine, but then once pushed to gitlab the build fails because publysher/hugo has a more recent version of hugo. If the Docker hub images were tagged I would be able to manage this versioning much better.