Replace ExceptionListener uses with ErrorListener

[APachecoDiSanti]

ExceptionListener has been deprecated in version 5.0 of symfony/http-kernel:
https://github.com/symfony/http-kernel/blob/master/CHANGELOG.md
The changelog recommends using ErrorListener instead.

[javiereguiluz]

These docs are very special because they belong to a special series called "Create your own framework". This is not really part of the Symfony Docs. So, I'm going to ask @wouterj and @xabbuh to see if they think we should change this. Thanks.

[wouterj]

I would say we should definitely change this. The code is broken, as the ExceptionListener no longer exists. Looking at the source code, I think both behave exactly the same. So these changes make perfect sense to me.

Thanks @APachecoDiSanti!

[javiereguiluz]

Thanks Agustín ... and congrats on your first Symfony Docs contribution!