code: function(cb) {
              log.log('git remote prune origin ' + repoDir);
              self.pruneOrigin(repoDir, function(err, stdout, stderr) {
                  if (err) {
                      log.warn(err.msg + ":", err.err.msg);
                  }
                  cb(null, {prune: {stdout: stdout, stderr: stderr}});
              });
          }
docs: Prune non-existing remote tracking branches