登录验证码的另外一种实现方法

验证码接口返回信息：

        var arrayBufferView = new Uint8Array(res.data);
        var blob = new Blob([arrayBufferView], { type: "image/jpeg" });
        var urlCreator = window.URL || window.webkitURL;
        captcha.url = urlCreator.createObjectURL(blob);