private void btnCapnhat_Click(object sender, EventArgs e)
        {
            DataGridViewRow row  = dataGridViewNguoiDung.CurrentRow;
            string          maso = row.Cells["colmaso"].Value.ToString();

            string username        = row.Cells["colusername"].Value.ToString();
            string loaitaikhoancol = row.Cells["colquyen"].Value.ToString();

            data.UpdateNguoiDung(username, loaitaikhoancol, maso);
            loadNguoiDung();
        }