Support symfony/yaml 4.x

[Nikerabbit]

I am using this library in a project where another component started depending on symfony/yaml 4.x. The latest release version of this library however only accepts 2.x or 3.x. I see that this has been changed in the master branch (1481b99), but this has not been released.

How about doing a release that supports symfony/yaml 4.x?

[philiplb]

A new release would be great! Currently I'm depending on "romaricdrigon/metayaml": "dev-master#1481b99679b29cbb50c88f3e10e4951ac64b8ad3",. This works but raises a warning on Symfony Insight.

[reedy]

And at this point, a release that supports symfony/yaml 5.x too...

[reedy]

Ping @romaricdrigon

[reedy]

It's been a few months... Worth trying again. Hey @romaricdrigon, I see you've been a bit active in other repos/projects in the last couple of months... Any chance of getting a release done here? Thanks!