Avoid deprecated notice when using symfony/config > 4.2

[odolbeau]

More information: https://github.com/symfony/symfony/blob/master/UPGRADE-4.2.md#config

[rvanlaak]

Tests are failing, but I see the test graph is quite big.

@Nyholm what about bumping to Symfony LTS 3.4 and PHP 7.2?

https://symfony.com/roadmap

That might also be a nice moment to put effort in a v1.0 release.

#252

https://github.com/php-translation/symfony-bundle/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc+milestone%3A%22Version+1.0%22

[odolbeau]

Tests were failing before this PR, I just removed some deprecation notices. I'll rebase this PR once master will be green if needed.

I'm not sure this PR should be linked to a symfony / PHP version bumping or a coming major release as it's not impacted nor impacting those changes.

Anyway I can propose another PR to bump requirements to "php":"^7.2" & "symfony/*": "^3.4 || ^4.0" if you want?

[Nyholm]

Hm. Yeah, maybe it is a good idea do use sf3.4 as minimum.

This PR looks good, (even though tests are failing).
Thank you.

[XWB]

@Nyholm Can you tag a new release that contains this change?

[hvt]

Would indeed be great if a new release could be tagged.