Update data_transformers.rst

Author: sela

form/data_transformers.rst

@@ -344,6 +344,7 @@ First, create the custom field type class::
     use AppBundle\Form\DataTransformer\IssueToNumberTransformer;
     use Doctrine\Common\Persistence\ObjectManager;
     use Symfony\Component\Form\AbstractType;
+    use Symfony\Component\Form\Extension\Core\Type\TextType;
     use Symfony\Component\Form\FormBuilderInterface;
     use Symfony\Component\OptionsResolver\OptionsResolver;