Update 08-add-to-window.problem.ts

As far as I understood, the test message itself is not a part of the exercise, so encountering it upon opening the exercise can be confusing.

Author: freiondrej-lokalise

src/02-globals/08-add-to-window.problem.ts

@@ -10,7 +10,7 @@ import { Equal, Expect } from "../helpers/type-utils";
  * interface to add a makeGreeting function
  */
 
-window.makeGreeting = () => "Hello!";
+window.makeGreeting = () => "Hello, world!";
 
 it("Should let you call makeGreeting from the window object", () => {
   expect(window.makeGreeting()).toBe("Hello, world!");