Update composer.json
Allow Symfony 2.4 and higher
Merge pull request #291 from Kunstmaan/feature/move-to-2.4-and-beyond

Allow Symfony 2.4 and higher
Merge remote-tracking branch 'origin/master' into issue14713-newdashboard

* origin/master:
  Allow Symfony 2.4 and higher
  Update composer.json