update description in error boundaries lesson 01 to match automated tests (#430)

Author: zelaznik

exercises/09.errors/01.problem.composition/index.tsx

@@ -98,7 +98,8 @@ function App() {
 
 // 🐨 create an ErrorFallback component here that accepts FallbackProps
 // and renders the error.message
-// The error message should be displayed in the format: "There was an error: [error message]"
+// The ErrorFallback component should return a React element with role="alert"
+// That element should contain text in the format: "There was an error: [error message]"
 // 💯 you can make it look nice if you want
 // 📜 https://github.com/bvaughn/react-error-boundary#errorboundary-with-fallbackcomponent-prop