Allow symfony 5

[Jeroeny]

#SymfonyHackday

[Steveb-p]

We should also add 5.0 to travis matrix.

[Jeroeny]

We should also add 5.0 to travis matrix.

Added, let me know what you think 👍.

[Steveb-p]

The are some conflicts with dev dependencies.

There should also be an expected test failure due to #984 not yet resolved :)

I’ll have a look once I’m in front of a pc.

[Jeroeny]

Indeed, it's this package: voryx/Thruway#329, for which I've made a PR.
Also PhpStan, but it looks like they already have a version WIP that removes a lot of dependencies, including symfony.

Edit: I was looking at phpstan/phpstan, but the development actually happens in phpstan-src. Which has 0.12 WIP that doesn't depend on symfony anymore.

[kuraobi]

@Jeroeny your PR was not sufficient so I did another one: voryx/Thruway#331 , but the maintainer says he prefers to remove the dependency to Symfony. So waiting for him to fork https://github.com/symfony/event-dispatcher and use that fork instead.

[kuraobi]

As there was no activity on voryx/Thruway#331 , I found another solution in #997 . Actually had a lot more to fix then, I detailed it in my PR.