minor #3890 [Components][HttpFoundation] use a placeholder for the co…

…nstructor arguments (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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[Components][HttpFoundation] use a placeholder for the constructor arguments

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

As suggested by @wouterj in #3869.

Commits
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631d673 use a placeholder for the constructor arguments

components/http_foundation/session_configuration.rst

@@ -83,7 +83,7 @@ Example usage::
     use Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage;
     use Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler;
 
-    $pdo = new \PDO('mysql:dbname=testdb;host=127.0.0.1');
+    $pdo = new \PDO(...);
     $storage = new NativeSessionStorage(array(), new PdoSessionHandler($pdo));
     $session = new Session($storage);