[TD-2639] <docs>: fix example about transaction in SQL execution.

documentation20/cn/12.taos-sql/docs.md

@@ -424,9 +424,9 @@ Query OK, 1 row(s) in set (0.001029s)
 taos> SHOW TABLES;
 Query OK, 0 row(s) in set (0.000946s)
 
-taos> INSERT INTO d1001 USING meters TAGS('Beijing.Chaoyang', 2);
+taos> INSERT INTO d1001 USING meters TAGS('Beijing.Chaoyang', 2) VALUES('a');
 
-DB error: invalid SQL: keyword VALUES or FILE required
+DB error: invalid SQL: 'a' (invalid timestamp) (0.039494s)
 
 taos> SHOW TABLES;
            table_name           |      created_time       | columns |          stable_name           |