protected function replaceLaravelServiceProviders($app_php)
    {
        $contents = file_get_contents($app_php);

        $strings = [
            'Illuminate\Mail\MailServiceProvider',
            'Illuminate\Queue\QueueServiceProvider'
        ];

		// Replacement to:
		//  - additionally support Google App Engine Queues,
        //  - additionally support Google App Engine Mail.
        $replacements = [
            'Shpasser\GaeSupport\Mail\GaeMailServiceProvider',
            'Shpasser\GaeSupport\Queue\QueueServiceProvider'
        ];

        $modified = str_replace($strings, $replacements, $contents);

        if ($modified === $contents)
        {
            return;
        }

        $this->createBackupFile($app_php);

        file_put_contents($app_php, $modified);

        $this->myCommand->info('Replaced the service providers in "app.php".');
    }