doc: update http URLs to https in CONTRIBUTING.md

PR-URL: #17261
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

CONTRIBUTING.md

@@ -221,9 +221,9 @@ In case of doubt, open an issue in the
 [issue tracker](https://github.com/nodejs/node/issues/) or contact one of the
 [project Collaborators](https://github.com/nodejs/node/#current-project-team-members).
 Node.js has two IRC channels:
-[#Node.js](http://webchat.freenode.net/?channels=node.js) for general help and
+[#Node.js](https://webchat.freenode.net/?channels=node.js) for general help and
 questions, and
-[#Node-dev](http://webchat.freenode.net/?channels=node-dev) for development of
+[#Node-dev](https://webchat.freenode.net/?channels=node-dev) for development of
 Node.js core specifically.
 
 ### Setting up your local environment