Require symfony/yaml ^4.4

Drupal core 9 requires symfony/yaml:^4.4.

It is impossible to install this module on a drupal 9 site because it requires symfony/yaml "~2.7.14|~2.8.7|~3.0.7|^3.1.1".

Please change the composer.json requirement to be: "symfony/yaml": "~2.7.14|~2.8.7|~3.0.7|^3.1.1|^4.4.9",