Adding Deprecation Warning to Vue Router | Challenge

# Introduction

In this challenge, we will fix an issue in the `vue-router v3.4.9` code. In version `vue-router v3.4.9`, a warning message was added to the `router.addRoutes()` method stating that it has been removed from Vue Router 4 and to use `router.addRoute()` instead. This challenge requires proficiency in the basic syntax of JavaScript.