Fix grammar in README about error handling (#433)

Author: WebCu

exercises/09.errors/README.mdx

@@ -10,8 +10,8 @@ your application will be removed from the page, leaving the user with a blank
 screen... Kind of awkward...
 
 The problem is, you can't just wrap your entire application in a `try`/`catch`
-because of the way JavaScript works. If you recall from earlier lessons, when
-then you'll remember this:
+because of the way JavaScript works. If you recall from earlier lessons, then 
+you'll remember this:
 
 ```tsx
 const element = (