Restore Lumen support

[erikn69]

Closes #728

Another option could be creating a especific event service provider only for lumen, like AuditingLumenEventServiceProvider::class

// AuditingServiceProvider.php
public function register()
{
  /////
  if ($this->app instanceof \Illuminate\Foundation\Application) {
      $this->app->register(AuditingEventServiceProvider::class);
  } else {
      $this->app->register(AuditingLumenEventServiceProvider::class);
  }
  /////

[MortenDHansen]

Lets get that out :)