doc: add yosuke-furukawa as collaborator

PR-URL: https://github.com/iojs/io.js/pull/1183


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Shigeki Ohtsu <ohtsu@iij.ad.jp>