doc: use HTTPS URL for suggested upstream remote

It's impossible to push to git:// URLs. PR-URL: #13602 Fixes: #13600 Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Refael Ackermann <refack@gmail.com> Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com> Reviewed-By: Brian White <mscdex@mscdex.net>

Author: seishun

CONTRIBUTING.md

@@ -30,7 +30,7 @@ locally.
 ```text
 $ git clone git@github.com:username/node.git
 $ cd node
-$ git remote add upstream git://github.com/nodejs/node.git
+$ git remote add upstream https://github.com/nodejs/node.git
 ```
 
 #### Which branch?