Fixes typo in README.mdx (#12)

Author: kenrett

exercises/03.client-components/README.mdx

@@ -17,7 +17,7 @@ enables mixing server-rendered components with client-rendered components.
 Server components should be used for things that come from the server and don't
 have client-side interactivity. For example, let's say you're building a todo
 list. The list of items can be rendered by the server. And the button to mark
-them as complete/uncomplete can even be rendered by the server as well.
+them as complete/incomplete can even be rendered by the server as well.
 
 However, if you want to implement optimistic UI for the checkbox to make the
 user experience feel faster, you're going to need to manage state on the client