code: def tags_newer(self, versions_file, majors):
          
          highest = versions_file.highest_version_major(majors)
          all = self.tags_get()
  
          newer = _newer_tags_get(highest, all)
  
          if len(newer) == 0:
              raise RuntimeError("No new tags found.")
  
          return newer
docs: Checks this git repo tags for newer versions.
          @param versions_file: a common.VersionsFile instance to
              check against.
          @param majors: a list of major branches to check. E.g. ['6', '7']
          @raise RuntimeError: no newer tags were found.
          @raise MissingMajorException: A new version from a newer major branch is
              exists, but hasn't been downloaded due to it not being in majors.