public function _getQRCode($expires_seconds,$type,$scene){
//获取票据json
$content=$this->_getTicket($expires_seconds,$type,$scene);
//json解码
$content=json_decode($content);
//获取ticket票据
$ticket=$content->ticket;
//获取二维码
return $this->_request("https://mp.weixin.qq.com/cgi-bin/showqrcode?ticket=".$ticket);
}