minor symfony#9297 Use "setAttribute" method (liviubalan)

This PR was merged into the 3.4 branch.

Discussion
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Use "setAttribute" method

See: http://api.symfony.com/3.4/Symfony/Component/Ldap/Entry.html#method_setAttribute

Commits
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676c1fc Use "setAttribute" method

Author: javiereguiluz

components/ldap.rst

@@ -126,7 +126,7 @@ delete existing ones::
     $query = $ldap->query('dc=symfony,dc=com', '(&(objectclass=person)(ou=Maintainers))');
     $result = $query->execute();
     $entry = $result[0];
-    $entry->addAttribute('email', array('[email protected]'));
+    $entry->setAttribute('email', array('[email protected]'));
     $em->update($entry);
 
     // Removing an existing entry