fixed sql in trigger

data/2.MySQL中阶/1.数据库组成/6. 触发器/audit.md

@@ -20,7 +20,8 @@ create table orders
 ```mysql
 create table orders_log
 (
-    id          int primary key auto_increment,
+    log_id          int primary key auto_increment,
+    id     int,
     item_id     int,
     amount      int,
     unit_price  decimal(12, 4),