[HttpKernel] Fix event dispatcher dependency

Update composer.json to account for #9792
bug #11113 [HttpKernel] Fix event dispatcher dependency (hacfi)

This PR was merged into the 2.5 branch.

Discussion
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[HttpKernel] Fix event dispatcher dependency

Update composer.json to account for #9792.

[Symfony\Component\HttpKernel\DependencyInjection\RegisterListenersPass](https://github.com/symfony/symfony/blob/2.5/src/Symfony/Component/HttpKernel/DependencyInjection/RegisterListenersPass.php#L14) extends `Symfony\Component\EventDispatcher\DependencyInjection\RegisterListenersPass` which exists only in 2.5

Commits
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3d2dd81 [HttpKernel] Fix event dispatcher dependency