Using perl:latest clashes with use of carton --deployment

[bestscarper]

I did a local build but used 'carton install' to avoid using the snapshot which I suspect is the root cause of the other issues.

I think the problem is that the Dockerfile uses 'perl:latest' as a base, and carton needs a (named) stable perl version in order to work reliably (CPAN modules often vary their deps on the Perl version).