Update Callback.rst

Author: snebes

reference/constraints/Callback.rst

@@ -300,5 +300,5 @@ Concrete callbacks receive an :class:`Symfony\\Component\\Validator\\Context\\Ex
 instance as only argument.
 
 Static or closure callbacks receive the validated object as the first argument
-and the :class:`Symfony\\Component\\Validator\\ExecutionContextInterface`
+and the :class:`Symfony\\Component\\Validator\\Context\\ExecutionContextInterface`
 instance as the second argument.