Add Dockerfile-prod highlighting

[TallOrderDev]

I'll dive into the code to see if I can help here, but I'd love to see a larger file selection for this add-on.

Current work around, rename file to just Dockerfile, edit, then rename back. Very Clunky though

[xamgore]

Well, you can change these lines to add a new file extension. So, the problem here is in the names: .Dockerfile-prod or .Dockerfile.prod, what is the best one? Anyway, you are welcome to make a PR. 😉