title: "Your configuration files are not serializable" error message after adding GELF logger in Laravel 5.6
body: <p>After adding GELF logging according to this how to <a href="https://medium.com/@vaidaslungis/setup-graylog-in-laravel-5-6-logging-d2276bcb9cfa" rel="nofollow noreferrer">https://medium.com/@vaidaslungis/setup-graylog-in-laravel-5-6-logging-d2276bcb9cfa</a>
  the <code>php artisan config:cache</code> command isn't working anymore.</p>
  
  <pre><code>The error message is:
  
  
  In ConfigCacheCommand.php line 68:
  
    Your configuration files are not serializable.  
  
  
  In config.php line 382:
  
    Call to undefined method Gelf\Publisher::__set_state()  
  </code></pre>
  
  <p>Is it still possible to cache the config? If so, what needs to be changed?</p>