in ComposerPlugin.php [57:63]
public function onPostAutoloadDump(Event $event) {
$args = $event->isDevMode() ? '' : ' --no-dev';
$executor = new ProcessExecutor($this->io);
$command = ProcessExecutor::escape($this->vendor.'/bin/hh-autoload.hack').
$args;
$executor->execute($command);
}