Highlight is broken in `heredocs` regions of the docker file

[romintomasetti]

When using heredocs sections in a Docker file, this extension does not seem to correctly highlight.

See the below screenshot. The comment is not colorized.

However, other linters I've tried manage to do it correctly. I'll mention https://github.com/hadolint/hadolint for instance.

Is there anything I can do to help you with this?