added birthdaytype namespace to fix #38 (#39)

Add BirthdayType namespace to fix #38

Author: Nick van der Zwet

Form/Type/FlexModelFormType.php

@@ -9,6 +9,7 @@
 use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
 use Symfony\Component\Form\Extension\Core\Type\DateTimeType;
 use Symfony\Component\Form\Extension\Core\Type\DateType;
+use Symfony\Component\Form\Extension\Core\Type\BirthdayType;
 use Symfony\Component\Form\Extension\Core\Type\FileType;
 use Symfony\Component\Form\Extension\Core\Type\IntegerType;
 use Symfony\Component\Form\Extension\Core\Type\NumberType;