🎨 优化代码，实现序列化接口

Author: binarywang

weixin-java-mp/src/main/java/me/chanjar/weixin/mp/bean/material/WxMpMaterialFileBatchGetResult.java

@@ -24,7 +24,9 @@ public String toString() {
   }
 
   @Data
-  public static class WxMaterialFileBatchGetNewsItem {
+  public static class WxMaterialFileBatchGetNewsItem implements Serializable {
+    private static final long serialVersionUID = -8300080343204117459L;
+
     private String mediaId;
     private Date updateTime;
     private String name;