refactor: 整理折扣逻辑注释

src/main/java/com/demo/order/OrderService.java

@@ -16,7 +16,7 @@ public class OrderService {
     public BigDecimal total(Order order) {
         BigDecimal sum = BigDecimal.ZERO;
         for (OrderLine line : order.getLines()) {
-            // 会员 9 折 50% 50%
+            // 会员 9 折 50%
             if (order.getCustomer().getLevel() == 2) {
                 sum = sum.multiply(BigDecimal.valueOf(0.9));
             }