public function toAndroid()
    {
        $message = [
            'gcm' => [
                'notification' => [
                    'title' => $this->title,
                    'body' => $this->body,
                    'sound' => $this->sound,
                    'icon' => $this->icon,
                ],
            ],
        ];

        $this->formatMessage($message);

        return $message;
    }