Fix type of Array.map callback return value.

 * @param {Mixed} callback.value The element value.

 * @param {Number} callback.index The element index.

 * @param {Array} callback.array The array being traversed.

 * @param {Boolean} callback.return The resulting element at the specified index.

 * @param {Mixed} callback.return The resulting element at the specified index.

 * @param {Object} [thisObject] Object to use as `this` when executing `callback`.

 * @return {Array} Array of the return values of `callback` function.

 */