Fix bug with losing list of branches when saving original article after branched
Fix bug with losing list of branches when saving original article after branched

- We would overwrite the list of branches in the metadata in the following
  scenario:
    - User a saves article x
    - User b creates branch of article x
    - article x now as 'b' in the list of branches
    - User a edits article x
    - This save would remove 'b' from list of branches, which is now fixed.

pluralsight/guides-cms,pluralsight/guides-cms,paulocheque/guides-cms,pluralsight/guides-cms,paulocheque/guides-cms,paulocheque/guides-cms