minor #8550 Missing use reference (matt9mg)

This PR was submitted for the 3.3 branch but it was merged into the 2.7 branch instead (closes #8550).

Discussion
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Missing use reference

This example is missing the use statement for a class that is created later on in the code examples.

Commits
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c6fa5d3 Missing use reference

Author: xabbuh

security/api_key_authentication.rst

@@ -22,11 +22,12 @@ value and then a User object is created::
     // src/AppBundle/Security/ApiKeyAuthenticator.php
     namespace AppBundle\Security;
 
+    use AppBundle\Security\ApiKeyUserProvider;
+    use Symfony\Component\HttpFoundation\Request;
     use Symfony\Component\Security\Core\Authentication\SimplePreAuthenticatorInterface;
+    use Symfony\Component\Security\Core\Authentication\Token\PreAuthenticatedToken;
     use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
     use Symfony\Component\Security\Core\Exception\AuthenticationException;
-    use Symfony\Component\Security\Core\Authentication\Token\PreAuthenticatedToken;
-    use Symfony\Component\HttpFoundation\Request;
     use Symfony\Component\Security\Core\User\UserProviderInterface;
     use Symfony\Component\Security\Core\Exception\BadCredentialsException;