Bump content models

This updates the content models gem to a version which stores SpecialistDocumentEditions in a separate collection. Given that content-api is already using this newer gem version, the publishing operation is not currently working (data is getting stored in one place and read from another).

This is the minimal set of changes to get publishing working for now.

Would be good if @elliotcm and @bestie could review and merge if it will not cause too many conflicts with the refactoring work in progress.