doc: add vkurchatkin as collaborator

PR-URL: https://github.com/iojs/io.js/pull/591


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>