minor #9370 Update dependency_injection.rst (flip111)

This PR was submitted for the 4.0 branch but it was merged into the 3.4 branch instead (closes #9370).

Discussion
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Update dependency_injection.rst

Add missing use of `Symfony\Component\HttpFoundation\RequestStack`

Commits
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9d3a4de Update dependency_injection.rst

Author: javiereguiluz

create_framework/dependency_injection.rst

@@ -10,9 +10,10 @@ to it::
     namespace Simplex;
 
     use Symfony\Component\EventDispatcher\EventDispatcher;
-    use Symfony\Component\Routing;
     use Symfony\Component\HttpFoundation;
+    use Symfony\Component\HttpFoundation\RequestStack;
     use Symfony\Component\HttpKernel;
+    use Symfony\Component\Routing;
 
     class Framework extends HttpKernel\HttpKernel
     {