minor symfony#9051 Update routing.rst (rickwest)

This PR was merged into the 4.0 branch.

Discussion
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Update routing.rst

Add trailing comma after last item of multiline array as suggested by symfony#8325

Commits
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b78ae51 Update routing.rst

Author: javiereguiluz

routing.rst

@@ -578,7 +578,7 @@ But if you pass extra ones, they will be added to the URI as a query string::
 
     $this->router->generate('blog', array(
         'page' => 2,
-        'category' => 'Symfony'
+        'category' => 'Symfony',
     ));
     // /blog/2?category=Symfony