Update Site source link

github/git-reference -> git/git-reference

Author: bry4n

_layouts/reference.html

@@ -27,7 +27,7 @@
           <!-- <li><a id="menu_cookbook" href="/cookbook.html">Cookbook</a></li> -->
 					<li><a id="menu_about" href="/about.html">About</a></li>
 					<li>&#167;</li>
-					<li><a href="https://github.com/github/git-reference">Site Source</a></li>
+					<li><a href="https://github.com/git/git-reference">Site Source</a></li>
         </ul>
         <br/>
         &nbsp;