[Serializer] Fix grammar issue

Author: sebpacz

components/serializer.rst

@@ -872,7 +872,7 @@ The Serializer component provides several built-in normalizers:
     This normalizer works with classes that implement
     :class:`Symfony\\Component\\Form\\FormInterface`.
 
-    It will get errors from the form and normalize them into an normalized array.
+    It will get errors from the form and normalize them into a normalized array.
 
 :class:`Symfony\\Component\\Serializer\\Normalizer\\ConstraintViolationListNormalizer`
     This normalizer converts objects that implement