doc: add calvinmetcalf to collaborators

PR-URL: #4218
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Ryan Graham <r.m.graham@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: calvinmetcalf

README.md

@@ -390,6 +390,7 @@ information about the governance of the Node.js project, see
 ### Collaborators
 
 * [brendanashworth](https://github.com/brendanashworth) - **Brendan Ashworth** <brendan.ashworth@me.com>
+* [calvinmetcalf](https://github.com/calvinmetcalf) - **Calvin Metcalf** <calvin.metcalf@gmail.com>
 * [ChALkeR](https://github.com/ChALkeR) - **Сковорода Никита Андреевич** <chalkerx@gmail.com>
 * [domenic](https://github.com/domenic) - **Domenic Denicola** <d@domenic.me>
 * [evanlucas](https://github.com/evanlucas) - **Evan Lucas** <evanlucas@me.com>