Error in CSRF example code snippet

Something's wrong when I tried this code:

`$formFactory = Forms::createFormFactoryBuilder()`
`        // ...`
`       ->addExtension(new CsrfExtension($csrfStorage))`
`        ->getFormFactory();`

Constructing a `CsrfExtension` requires a `CsrfTokenManagerInterface` as an argument (see symfony/form/Extension/Csrf/CsrfExtension.php, line 24).

The `$csrfStorage` in `addExtension(new CsrfExtension($csrfStorage)`, has a class that implements `TokenStorageInterface` (see symfony/security-csrf/TokenStorage/SessionStorageToken.php,  line 22).

So I replaced it with `$csrfManager` that has class that implement `CsrfTokenManagerInterface`. (see symfony/security-csrf/CsrfTokenManager.php, line 24)

Author: makoru-hikage

components/form.rst

@@ -137,7 +137,7 @@ The following snippet adds CSRF protection to the form factory::
 
     $formFactory = Forms::createFormFactoryBuilder()
         // ...
-        ->addExtension(new CsrfExtension($csrfStorage))
+        ->addExtension(new CsrfExtension($csrfManager))
         ->getFormFactory();
 
 Internally, this extension will automatically add a hidden field to every