TreeBuilder::root deprecated symfony 4

[Herz3h]

Just creating the issue to link it to PR later:

The "Symfony\Component\Config\Definition\Builder\TreeBuilder::root()" method called for the "faker" configuration is deprecated since Symfony 4.3, pass the root name to the constructor instead.

Example fix:

https://github.com/symfony/monolog-bundle/pull/281/commits/45742f1a97291edd1401ecb58024488bbd793038

[Herz3h]

Any way to get this merged @willdurand ?