fixed the form example to not use deprecated methods

doc/providers/form.rst

@@ -110,8 +110,7 @@ example::
             ))
             ->getForm();
 
-        if ('POST' == $request->getMethod()) {
-            $form->bind($request);
+        $form->handleRequest($request);
 
         if ($form->isValid()) {
             $data = $form->getData();
@@ -121,7 +120,6 @@ example::
             // redirect somewhere
             return $app->redirect('...');
         }
-        }
 
         // display the form
         return $app['twig']->render('index.twig', array('form' => $form->createView()));