【OpenHarmony开源贡献者计划2022】update zh-cn/application-dev/database/database-relational-guidelines.md.

多了一个逗号，删掉
Signed-off-by: xia-junapple<junxiag@isoftstone.com >
Signed-off-by: N夏军 <junxiag@isoftstone.com>

zh-cn/application-dev/database/database-relational-guidelines.md

@@ -215,7 +215,7 @@
 
     ```js
     var u8 = new Uint8Array([1, 2, 3])
-    const valueBucket = {"name": "Tom", "age": 18, "salary": 100.5, "blobType": u8,}
+    const valueBucket = {"name": "Tom", "age": 18, "salary": 100.5, "blobType": u8}
     let insertPromise = rdbStore.insert("test", valueBucket)
     ```