Approach of conversion for array in query to avoid breaking change (vuejs#817)

* Approach of conversion for array in query to avoid breaking change

* Minor revise

* Minor revise

* Explain more clearly

* Minor revise

* Use computed property instead

* Update migration-vue-router.md

* Insist in adding a computed property

* Update migration-vue-router.md

Author: KingMario

src/v2/guide/migration-vue-router.md

@@ -236,6 +236,23 @@ if (route.meta.requiresAuth) {
 </div>
 {% endraw %}
 
+### [] Syntax for Arrays in Queries <sup>removed</sup>
+
+When passing arrays to query parameters the QueryString syntax is no longer `/foo?users[]=Tom&users[]=Jerry`, instead, the new syntax is `/foo?users=Tom&users=Jerry`. Internally, `$route.query.users` will still be an Array, but if there's only one parameter in the query: `/foo?users=Tom`, when directly accessing this route, there's no way for the router to know if we were expecting `users` to be an Array. Because of this, consider adding a computed property and replacing every reference of `$route.query.users` with it:
+
+```javascript
+export default {
+  // ...
+  computed: {
+    // users will always be an array
+    users () {
+      const users = this.$route.query.users
+      return Array.isArray(users) ? users : [users]
+    }
+  }
+}
+```
+
 ## Route Matching
 
 Route matching now uses [path-to-regexp](https://github.com/pillarjs/path-to-regexp) under the hood, making it much more flexible than previously.