minor #4781 [Serializer] Bad variable name in example (arno14)

This PR was submitted for the master branch but it was merged into the 2.6 branch instead (closes #4781).

Discussion
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[Serializer] Bad variable name in example

Commits
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ef4abd1 Typo in Serializer doc

Author: wouterj

components/serializer.rst

@@ -310,7 +310,7 @@ when such a case is encountered::
     $org->setName('Les-Tilleuls.coop');
     $org->setMembers(array($member));
 
-    $member->setOrganization($kevin);
+    $member->setOrganization($org);
 
     echo $serializer->serialize($org, 'json'); // Throws a CircularReferenceException