doc: fix typo in CONTRIBUTING.md
doc: fix typo in CONTRIBUTING.md

PR-URL: https://github.com/nodejs/io.js/pull/1755
Reviewed-By: Evan Lucas <ad0310dc5270cefb6ee6879263270aed9b1e9982@me.com>
Reviewed-By: Roman Reiss <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@silverwind.io>
Reviewed-By: Jeremiah Senkpiel <f1782d15e31ad502ea2c097c21cc235811d0cb7c@rocketmail.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node