Update file-upload.md (#1345)

Author: brettins

core/file-upload.md

@@ -186,7 +186,7 @@ use Symfony\Component\Serializer\Normalizer\NormalizerAwareInterface;
 use Symfony\Component\Serializer\Normalizer\NormalizerAwareTrait;
 use Vich\UploaderBundle\Storage\StorageInterface;
 
-final class MediaObjectNormalizer implements ContextAwareNormalizerInterface
+final class MediaObjectNormalizer implements ContextAwareNormalizerInterface, NormalizerAwareInterface
 {
     use NormalizerAwareTrait;