doc: fix missing newline character

PR-URL: #16447
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Yuta Hiroto <[email protected]>
Reviewed-By: Anatoli Papirovski <[email protected]>
Reviewed-By: Gireesh Punathil <[email protected]>

Author: watilde

COLLABORATOR_GUIDE.md

@@ -677,4 +677,4 @@ LTS working group and the Release team.
 [backporting guide]: doc/guides/backporting-to-release-lines.md
 [Stability Index]: doc/api/documentation.md#stability-index
 [Enhancement Proposal]: https://github.com/nodejs/node-eps
-[git-username]: https://help.github.com/articles/setting-your-username-in-git/
+[git-username]: https://help.github.com/articles/setting-your-username-in-git/