minor symfony#8395 Update business-logic.rst (RaitoCZ)

This PR was merged into the 3.3 branch.

Discussion
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Update business-logic.rst

previous example didn't show the usage of service passed via argument but fetching via $this->get.

Commits
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a5d2304 Update business-logic.rst

Author: xabbuh

best_practices/business-logic.rst

@@ -121,7 +121,7 @@ Now you can use the custom slugger in any controller class, such as the
         // $slugger = $this->get('app.slugger');
 
         if ($form->isSubmitted() && $form->isValid()) {
-            $slug = $this->get('app.slugger')->slugify($post->getTitle());
+            $slug = $slugger->slugify($post->getTitle());
             $post->setSlug($slug);
 
             // ...