UPGRADE FROM 3.3 to 3.4
=======================
Finder
------
* The `Symfony\Component\Finder\Iterator\FilterIterator` class has been
deprecated and will be removed in 4.0 as it used to fix a bug which existed
before version 5.5.23/5.6.7
Validator
---------
* not setting the `strict` option of the `Choice` constraint to `true` is
deprecated and will throw an exception in Symfony 4.0