Fix deprecation messages

[AntseN]

First of all thanks for this bundle.
Since symfony 5 is out, it would be great to fix the deprecation messages coming from this bundle :

The "Mgilet\NotificationBundle\Controller\NotificationController" class extends "Symfony\Bundle\FrameworkBundle\Controller\Controller" that is deprecated since Symfony 4.2, use "Symfony\Bundle\FrameworkBundle\Controller\AbstractController" instead.

Which shouldnt be too hard to fix ^^

[maximilienGilet]

Hi, thanks for the tip-off,

Unfortunately I don't use the bundle anymore, so feel free to create a pull request :)