minor #12962 [SecurityBundle] remove short array syntax (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

[SecurityBundle] remove short array syntax

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

The short array syntax was introduced in PHP 5.4 and therefore leads
to failing tests when executed in PHP 5.3 environments.

Commits
-------

697ce4d remove short array syntax

src/Symfony/Bundle/SecurityBundle/Tests/DependencyInjection/SecurityExtensionTest.php

@@ -80,13 +80,13 @@ class SecurityExtensionTest extends \PHPUnit_Framework_TestCase
 
         $container->loadFromExtension('security', array(
             'providers' => array(
-                'my_foo' => array('foo' => []),
+                'my_foo' => array('foo' => array()),
             ),
 
             'firewalls' => array(
                 'some_firewall' => array(
                     'pattern' => '/.*',
-                    'http_basic' => [],
+                    'http_basic' => array(),
                 ),
             ),
         ));