Update the links for the groupme protocol to the active repository

Testing Done:
Ran the devserver and verified everything looked okay.

Reviewed at
title: Development
date: 2019-01-15T03:38:25.000Z
anchor: development
weight: 90
lastmod: 2019-01-21T22:34:09.000Z
In this section you'll find information related to developing Pidgin. Keep in
mind that since Pidgin is a huge project there's a lot of content here so try
not to feel overwhelmed by it.