尝试发送推送通知会引发异常？

Question

I'm trying create a PHP class to send Push Notification. When I try send push doesn't works an throws an exception of syntax error and I can't find this error. I'm using PHP 5.3.28.

How could I solve it ?

Pusher

<?php

class Pusher{
    const GOOGLE_GCM_URL = 'https://android.googleapis.com/gcm/send';
    private $apiKey;
    private $proxy;
    private $output;
    public function __construct($apiKey, $proxy = null)
    {
        $this->apiKey = $apiKey;
        $this->proxy  = $proxy;
    }
    /**
     * @param string|array $regIds
     * @param string $data
     * @throws \Exception
     */
    public function notify($regIds, $data)
    {
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, self::GOOGLE_GCM_URL);
        if (!is_null($this->proxy)) {
            curl_setopt($ch, CURLOPT_PROXY, $this->proxy);
        }
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_HTTPHEADER, $this->getHeaders());
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $this->getPostFields($regIds, $data));
        $result = curl_exec($ch);
        if ($result === false) {
            throw new \Exception(curl_error($ch));
        }
        curl_close($ch);
        $this->output = $result;
    }
    /**
     * @return array
     */
    public function getOutputAsArray()
    {
        return json_decode($this->output, true);
    }
    /**
     * @return object
     */
    public function getOutputAsObject()
    {
        return json_decode($this->output);
    }

    private function getHeaders(){
        return [
            'Authorization: key=' . $this->apiKey,
            'Content-Type: application/json'
        ];
    }

    private function getPostFields($regIds, $data){
        $fields = [
            'registration_ids' => is_string($regIds) ? [$regIds] : $regIds,
            'data'             => is_string($data) ? ['message' => $data] : $data,
        ];
        return json_encode($fields, JSON_HEX_TAG | JSON_HEX_APOS | JSON_HEX_QUOT | JSON_HEX_AMP | JSON_UNESCAPED_UNICODE);
    }
}

Exception

Fatal Error
Error: syntax error, unexpected '[' 
File: /app/Plugin/Push/Pusher.php   
Line: 60

At line 60 have

private function getHeaders(){
            return [
                'Authorization: key=' . $this->apiKey,
                'Content-Type: application/json'
            ];
        }