doc: add who to CC list for dgram

PR-URL: https://github.com/nodejs/node/pull/11035
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>

doc/onboarding-extras.md

@@ -9,6 +9,7 @@
 | `lib/child_process` | @bnoordhuis, @cjihrig |
 | `lib/cluster` | @bnoordhuis, @cjihrig, @mcollina |
 | `lib/{crypto,tls,https}` | @nodejs/crypto |
+| `lib/dgram` | @cjihrig, @mcollina |
 | `lib/domains` | @misterdjules |
 | `lib/fs`, `src/{fs|file}` | @nodejs/fs |
 | `lib/{_}http{*}` | @nodejs/http |