Update outdated link to avoid redirect (#4218)

content/docs/code-splitting.md

@@ -174,7 +174,7 @@ Deciding where in your app to introduce code splitting can be a bit tricky. You
 
 A good place to start is with routes. Most people on the web are used to page transitions taking some amount of time to load. You also tend to be re-rendering the entire page at once so your users are unlikely to be interacting with other elements on the page at the same time.
 
-Here's an example of how to setup route-based code splitting into your app using libraries like [React Router](https://reacttraining.com/react-router/) with `React.lazy`.
+Here's an example of how to setup route-based code splitting into your app using libraries like [React Router](https://reactrouter.com/) with `React.lazy`.
 
 ```js
 import React, { Suspense, lazy } from 'react';