docs: prefer shorter demo

src/sidebar/README.md

@@ -71,10 +71,7 @@ import { Toast } from 'vant';
 export default {
   setup() {
     const active = ref(0);
-    const onChange = (index) => {
-      Toast(`Title ${index + 1}`);
-    };
-
+    const onChange = (index) => Toast(`Title ${index + 1}`);
     return {
       active,
       onChange,

src/sidebar/README.zh-CN.md

@@ -79,10 +79,7 @@ import { Toast } from 'vant';
 export default {
   setup() {
     const active = ref(0);
-    const onChange = (index) => {
-      Toast(`标签名 ${index + 1}`);
-    };
-
+    const onChange = (index) => Toast(`标签名 ${index + 1}`);
     return {
       active,
       onChange,

src/sidebar/demo/index.vue

@@ -67,9 +67,7 @@ export default {
       active4: 0,
     });
 
-    const onChange = (index: number) => {
-      Toast(`${t('title')} ${index + 1}`);
-    };
+    const onChange = (index: number) => Toast(`${t('title')} ${index + 1}`);
 
     return {
       ...toRefs(state),