minor symfony#10181 Update form_customization.rst (apirec)

This PR was merged into the 4.1 branch.

Discussion
----------

Update form_customization.rst

Fixed a small error.

Commits
-------

fa18271 Update form_customization.rst

Author: weaverryan

form/form_customization.rst

@@ -20,7 +20,7 @@ method:
 
     {{ form_row(form.age) }}
 
-You can also render each of the three parts of the field individually:
+You can also render each of the four parts of the field individually:
 
 .. code-block:: html+twig