Fix warnings on Node 6

[joaosa]

While running this, I was getting some warnings on the form

(node) v8::ObjectTemplate::Set() with non-primitive values is deprecated
(node) and will stop working in the next major release.

==== JS stack trace =========================================

Security context: 0x13ca8d8c9fa9 <JS Object>#0#
...

Updating Chokidar fixed this :)

[shime]

Thanks!