minor #11011 Replace Controller with AbstractController (krisdante)

This PR was merged into the 4.2 branch.

Discussion
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Replace Controller with AbstractController

As of Symfony 4.2 Symfony\Bundle\FrameworkBundle\Controller\Controller is depreciated in favor of Symfony\Bundle\FrameworkBundle\Controller\AbstractController. To reflect this update I tweaked the section of getting parameter, as it slightly changed, and getParameter is no longer there on the container,

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Commits
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c8eae69 Replace Controller with AbstractController

Author: javiereguiluz

service_container.rst

@@ -534,8 +534,8 @@ You can also fetch parameters directly from the container::
     {
         // ...
 
-        // this ONLY works if you extend the base Controller
-        $adminEmail = $this->container->getParameter('admin_email');
+        // this ONLY works if you extend the base AbstractController
+        $adminEmail = $this->container->get('parameter_bag')->get('admin_email');
 
         // or a shorter way!
         // $adminEmail = $this->getParameter('admin_email');