Adding support for node 4.*

[enchev]

From @prijindal on September 24, 2015 4:50

A lot of people are upgrading to the latest node version 4.0
but nativescript can't be installed on node 4.
Any plans to provide its support for latest version?

Copied from original issue: NativeScript/NativeScript#813

[prijindal]

It is mainly due to these three dependecies:
bufferutil,
ref,
ref-struct(which uses ref),
utf-8-validate,
ws ( which uses bufferutil)

All of these are using an earlier version of nan (1.5 or 1.8) which does not support node 4.0.0 but nan's latest version 2.0 does