:art: add xml annotation

weixin-java-pay/src/main/java/com/github/binarywang/wxpay/bean/result/WxWithholdResult.java

@@ -20,6 +20,7 @@ import java.io.Serializable;
 @Data
 @AllArgsConstructor
 @NoArgsConstructor
+@XStreamAlias("xml")
 public class WxWithholdResult extends BaseWxPayResult implements Serializable {
 
   private static final long serialVersionUID = 1L;