doc: add JungMinu to collaborators

PR-URL: https://github.com/nodejs/node/pull/4143


Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <http://www.cjihrig.com

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Reviewed-By: Kat Marchán <kzm@sykosomatic.org>
Reviewed-By: James M Snell <jasnell@gmail.com>