public function onPostAutoloadDump(Event $event) {
    $args = $event->isDevMode() ? '' : ' --no-dev';
    $finder = new ExecutableFinder();
    $hhvm = $finder->find('hhvm', 'hhvm');
    $executor = new ProcessExecutor($this->io);
    $command = $hhvm . ' ' . ProcessExecutor::escape($this->vendor.'/bin/hh-autoload.hack') . $args;
    $executor->execute($command);
  }