Deprecate G+ community in favor of StackOverflow.

website/index.html

@@ -257,7 +257,7 @@ limitations under the License.</pre>
               </ul>
               <ul class="nav nav-pills nav-stacked secondary">
                 <li><a href="javadoc/index.html">Javadoc</a></li>
-                <li><a href="https://plus.google.com/communities/109244258569782858265/stream/63e22a6d-b165-489a-92ab-d35f942beb5b">Google+ Community</a></li>
+                <li><a href="http://stackoverflow.com/questions/tagged/retrofit?sort=active">StackOverflow</a></li>
               </ul>
             </div>
           </div>