set flow item's width to 100%

Signed-off-by: Nzcdqs <junfeng.lijunfeng@huawei.com>
Change-Id: Iab0e88d01d24c512459d2049aa6d6b104c46f4ec

zh-cn/application-dev/reference/arkui-ts/ts-container-waterflow.md

@@ -264,7 +264,7 @@ struct WaterflowDemo {
                 .layoutWeight(1)
             }
           }
-          .width(this.itemWidthArray[item])
+          .width('100%')
           .height(this.itemHeightArray[item])
           .backgroundColor(this.colors[item % 5])
         }, item => item)