doc: add calvinmetcalf to collaborators
doc: add calvinmetcalf to collaborators

PR-URL: https://github.com/nodejs/node/pull/4218
Reviewed-By: Jeremiah Senkpiel <f1782d15e31ad502ea2c097c21cc235811d0cb7c@rocketmail.com>
Reviewed-By: Ryan Graham <cdcde8092c3401c6195519cb357ce33fe9f16916@gmail.com>
Reviewed-By: Matteo Collina <9e82044cc2ddcb8c7b7cca6ead2a720852437b44@gmail.com>

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