docs: prefer shorter demo

src/swipe/README.md

@@ -76,9 +76,7 @@ import { Toast } from 'vant';
 
 export default {
   setup() {
-    const onChange = (index) => {
-      Toast('Current Swipe index:' + index);
-    };
+    const onChange = (index) => Toast('Current Swipe index:' + index);
     return { onChange };
   },
 };

src/swipe/README.zh-CN.md

@@ -80,9 +80,7 @@ import { Toast } from 'vant';
 
 export default {
   setup() {
-    const onChange = (index) => {
-      Toast('当前 Swipe 索引：' + index);
-    };
+    const onChange = (index) => Toast('当前 Swipe 索引：' + index);
     return { onChange };
   },
 };

src/swipe/demo/index.vue

@@ -98,10 +98,7 @@ export default {
       'https://img.yzcdn.cn/vant/apple-4.jpg',
     ];
 
-    const onChange1 = (index) => {
-      Toast(t('message') + index);
-    };
-
+    const onChange1 = (index) => Toast(t('message') + index);
     const onChange2 = (index) => {
       current.value = index;
     };