listSubTreeBFS only lists direct children, not subchildren.

[alexmakarevich]

Hello.

I've spotted a bug in the listSubTreeBFS method.

It's supposed to return a list of all children and their subchildren of a node, but since the bump of async, this is no longer the case.

Prior usage of async.reduce "faked recursion" by mutating the accumulator (referred to as "memo" by async).
Newer versions of async disregard this mutation, breaking the functionality of listSubTreeBFS.