[Doc] use relative path for links (#4093)

src/cell/README.md

@@ -59,7 +59,7 @@ Vue.use(Cell).use(CellGroup);
 
 ```html
 <van-cell-group>
-  <van-cell title="URL" is-link url="//youzan.github.io/vant/mobile.html" />
+  <van-cell title="URL" is-link url="/vant/mobile.html" />
   <van-cell title="Vue Router" is-link to="index" />
 </van-cell-group>
 ```

src/cell/README.zh-CN.md

@@ -62,7 +62,7 @@ Vue.use(Cell).use(CellGroup);
 可以通过`url`属性进行 URL 跳转，或通过`to`属性进行路由跳转
 
 ```html
-<van-cell title="URL 跳转" is-link url="//youzan.github.io/vant/mobile.html" />
+<van-cell title="URL 跳转" is-link url="/vant/mobile.html" />
 <van-cell title="路由跳转" is-link to="index" />
 ```
 

src/cell/demo/index.vue

@@ -62,7 +62,7 @@
       <van-cell
         :title="$t('urlRoute')"
         is-link
-        url="//youzan.github.io/vant/mobile.html"
+        url="/vant/mobile.html"
       />
       <van-cell
         :title="$t('vueRoute')"