fix(enums3): modify message string in test

Otherwise it won't actually test the change of state.message and
it would fail to check if the user missed changing state.message

This happened to me as I had a catch-all line in `match`

Author: pksadiq

exercises/enums/enums3.rs

@@ -59,14 +59,14 @@ mod tests {
             message: "hello world".to_string(),
         };
         state.process(Message::ChangeColor(255, 0, 255));
-        state.process(Message::Echo(String::from("hello world")));
+        state.process(Message::Echo(String::from("Hello world!")));
         state.process(Message::Move(Point { x: 10, y: 15 }));
         state.process(Message::Quit);
 
         assert_eq!(state.color, (255, 0, 255));
         assert_eq!(state.position.x, 10);
         assert_eq!(state.position.y, 15);
         assert_eq!(state.quit, true);
-        assert_eq!(state.message, "hello world");
+        assert_eq!(state.message, "Hello world!");
     }
 }