code: function mapValuesLimit(obj, limit, iteratee, callback) {
      callback = once(callback);
      var newObj = {};
      var _iteratee = wrapAsync(iteratee)
      return eachOfLimit(limit)(obj, (val, key, next) => {
          _iteratee(val, key, (err, result) => {
              if (err) return next(err);
              newObj[key] = result;
              next(err);
          });
      }, err => callback(err, newObj));
  }
docs: The same as [`mapValues`]{@link module:Collections.mapValues} but runs a maximum of `limit` async operations at a
  time.
  
  @name mapValuesLimit
  @static
  @memberOf module:Collections
  @method
  @see [async.mapValues]{@link module:Collections.mapValues}
  @category Collection
  @param {Object} obj - A collection to iterate over.
  @param {number} limit - The maximum number of async operations at a time.
  @param {AsyncFunction} iteratee - A function to apply to each value and key
  in `coll`.
  The iteratee should complete with the transformed value as its result.
  Invoked with (value, key, callback).
  @param {Function} [callback] - A callback which is called when all `iteratee`
  functions have finished, or an error occurs. `result` is a new object consisting
  of each key from `obj`, with each transformed value on the right-hand side.
  Invoked with (err, result).
  @returns {Promise} a promise, if no callback is passed