文件下载提示：致命错误: Call to undefined function think\response\finfo_open()

$document_root = $_SERVER['DOCUMENT_ROOT'];
$path = $document_root . '/upload/store/store.png';
$download =  new \think\response\Download($path);
return $download->name('测试下载.png');

错误原因：未安装fileinfo扩展 

安装完成后，重启nginx，重新测试