fastadmin验证码不显示解决办法

找下以下文件 

vendor/topthink/think-captcha/src/CaptchaController.php

修改第20行.在后面加上

ob_clean();

namespace think\captcha;

use think\Config;

class CaptchaController
{
    public function index($id = "")
    {
        $captcha = new Captcha((array)Config::get('captcha'));ob_clean();  //加在这里
        return $captcha->entry($id);
    }
}