Fix typo load-the-state-from-the-session.md (#746)

Trivial fix, but instructions mentioned "App.js" instead of "App.tsx"

_chapters/load-the-state-from-the-session.md

@@ -88,7 +88,7 @@ Since loading the user session is an asynchronous process, we want to ensure tha
 
 We'll conditionally render our app based on the `isAuthenticating` flag.
 
-{%change%} Replace the `return` statement in `src/App.js` with the following.
+{%change%} Replace the `return` statement in `src/App.tsx` with the following.
 
 {% raw %}