docs: fix quickstart

README.md

@@ -58,7 +58,7 @@ import { Button } from 'vant';
 import 'vant/lib/index.css';
 
 const app = createApp();
-Vue.use(Button);
+app.use(Button);
 ```
 
 See more in [Quickstart](https://youzan.github.io/vant#/en-US/quickstart).

README.zh-CN.md

@@ -61,7 +61,7 @@ import { Button } from 'vant';
 import 'vant/lib/index.css';
 
 const app = createApp();
-Vue.use(Button);
+app.use(Button);
 ```
 
 vant 也支持按需引入、CDN 引入等方式，详细说明见 [快速上手](https://vant-contrib.gitee.io/vant#/zh-CN/quickstart).

docs/markdown/quickstart.en-US.md

@@ -121,7 +121,7 @@ The easiest way to use Vant is to include a CDN link in the html file, after whi
   vant.Toast('Message');
 
   // Register Lazyload directive
-  Vue.use(vant.Lazyload);
+  // app.use(vant.Lazyload);
 </script>
 ```
 

docs/markdown/quickstart.zh-CN.md

@@ -139,7 +139,7 @@ app.use(Vant);
 
   // 通过 CDN 引入时不会自动注册 Lazyload 组件
   // 可以通过下面的方式手动注册
-  Vue.use(vant.Lazyload);
+  // app.use(vant.Lazyload);
 </script>
 ```