[Validator] Add a comma after the last array item in a multi-line array

Author: wkania

validation/raw_values.rst

@@ -88,7 +88,7 @@ Validation of arrays is possible using the ``Collection`` constraint::
                 new Assert\Collection([
                     'slug' => [
                         new Assert\NotBlank(),
-                        new Assert\Type(['type' => 'string'])
+                        new Assert\Type(['type' => 'string']),
                     ],
                     'label' => [
                         new Assert\NotBlank(),