onEachDirectory callbacks only top level directory

[하도영]

Hi, really thanks for good library.

When testing onEachDirectory callback, it only returns top level directory.
I tested on nodejs v10, directory-tree v2.2.0, installed via npm.

I think onEachDirectory callback parameter is missing when calling directoryTree recursively.

node-directory-tree/lib/directory-tree.js

Line 99 in 5f2db29

 .map(child => directoryTree(PATH.join(path, child), options, onEachFile)) 

[Mihnea Dobrescu-Balaur]

Hi, good find! Feel free to submit a PR :).