Fix bad Documentation link in Playground.

Playground/debug.html

@@ -117,7 +117,7 @@
                 <li><a href="http://www.html5gamedevs.com/forum/16-babylonjs/">Forum</a></li>
                 <li><a href="https://babylonjs.azurewebsites.net/sandbox">Sandbox</a></li>
                 <li><a href="https://github.com/BabylonJS/Babylon.js/wiki">Wiki</a></li>
-                <li><a href="http://www.sokrate.fr/documentation/babylonjs/index.html">Documentation</a></li>
+                <li><a href="https://doc.babylonjs.com">Documentation</a></li>
             </ul>
         </div>
     </div>

Playground/index-local.html

@@ -85,7 +85,7 @@
                 <li><a href="http://www.html5gamedevs.com/forum/16-babylonjs/">Forum</a></li>
                 <li><a href="http://www.babylonjs.com/sandbox">Sandbox</a></li>
                 <li><a href="https://github.com/BabylonJS/Babylon.js/wiki">Wiki</a></li>
-                <li><a href="http://www.sokrate.fr/documentation/babylonjs/index.html">Documentation</a></li>
+                <li><a href="https://doc.babylonjs.com">Documentation</a></li>
             </ul>
         </div>
     </div>

Playground/index.html

@@ -116,7 +116,7 @@
                 <li><a href="http://www.html5gamedevs.com/forum/16-babylonjs/">Forum</a></li>
                 <li><a href="https://babylonjs.azurewebsites.net/sandbox">Sandbox</a></li>
                 <li><a href="https://github.com/BabylonJS/Babylon.js/wiki">Wiki</a></li>
-                <li><a href="http://www.sokrate.fr/documentation/babylonjs/index.html">Documentation</a></li>
+                <li><a href="https://doc.babylonjs.com">Documentation</a></li>
             </ul>
         </div>
     </div>