Unable to use this extension with Symfony 4.0

The dependency `henrikbjorn/lurker` does not allow to use the Symfony 4.0 event-dispatcher and the last change have 2 years ago.

Can you change this dependencies for allow use this extension with SF 4.0 ?

Link to the `henrikbjorn/lurker` pull request for add SF4.0 support: https://github.com/flint/Lurker/pull/29