doc: add romankl to collaborators

PR-URL: https://github.com/nodejs/node/pull/3725


Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
Reviewed-By: Myles Borins <mborins@us.ibm.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>