fix(@vant/cli): doc preview page cannot scroll to the correct anchor (#7745)

Co-authored-by: caoenze <caoenze@didichuxing.com>

packages/vant-markdown-loader/src/index.js

@@ -30,9 +30,7 @@ export default {
       if (event.target.id) {
         this.$router.push({
           name: this.$route.name,
-          query: {
-            anchor: event.target.id
-          }
+          hash: '#' + event.target.id
         })
       }
     }