code: @Override
      public NutMap pay_unifiedorder(String key, WxPayUnifiedOrder wxPayUnifiedOrder) {
          String url = payBase + "/pay/unifiedorder";
          Map<String, Object> params = Lang.obj2map(wxPayUnifiedOrder);
          return this.postPay(url, key, params);
      }
docs: 统一下单
  
  @param key
  商户KEY
  @param wxPayUnifiedOrder
  交易订单内容
  @return