Update ldap.rst

Add single quotes in filter option documentation

Author: jljohnstone

components/ldap.rst

@@ -117,7 +117,7 @@ to the ``LDAP_SCOPE_BASE`` scope of :phpfunction:`ldap_read`) and ``SCOPE_ONE``
 
 Use the ``filter`` option to only retrieve some specific attributes:
 
-    $query = $ldap->query('dc=symfony,dc=com', '...', ['filter' => ['cn, mail']);
+    $query = $ldap->query('dc=symfony,dc=com', '...', ['filter' => ['cn', 'mail']);
 
 Creating or Updating Entries
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