bug #3473 Update proxy_examples.rst (AZielinski)

This PR was submitted for the 2.4 branch but it was merged into the 2.3 branch instead (closes #3473).

Discussion
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Update proxy_examples.rst

Code sample modified to reflect the actual usage

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?    | no
| Applies to     | 2.1+
| Fixed tickets | none

Commits
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44498f2 Update proxy_examples.rst

cookbook/session/proxy_examples.rst

@@ -10,10 +10,10 @@ is injected into the proxy and registered with the session storage driver::
 
     use Symfony\Component\HttpFoundation\Session\Session;
     use Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage;
-    use Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionStorage;
+    use Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler;
 
-    $proxy = new YourProxy(new PdoSessionStorage());
-    $session = new Session(new NativeSessionStorage($proxy));
+    $proxy = new YourProxy(new PdoSessionHandler());
+    $session = new Session(new NativeSessionStorage(array(), $proxy));
 
 Below, you'll learn two real examples that can be used for ``YourProxy``:
 encryption of session data and readonly guest session.