Update filewalker.js to prevent usage of process.nextTick

in latest version of node process.nextTick gives following warning.

(node) warning: Recursive process.nextTick detected. This will break in the next version of node. Please use setImmediate for recursive deferral.

because of this sometimes code was breaking.
Merge pull request #5 from nitinhayaran/master

Update filewalker.js to prevent usage of process.nextTick in later version of node