fix(enums3): Update Message::ChangeColor to take a tuple. (#457)

Author: yukihane

exercises/enums/enums3.rs

@@ -51,7 +51,7 @@ mod tests {
             position: Point{ x: 0, y: 0 },
             color: (0, 0, 0)
         };
-        state.process(Message::ChangeColor(255, 0, 255));
+        state.process(Message::ChangeColor((255, 0, 255)));
         state.process(Message::Echo(String::from("hello world")));
         state.process(Message::Move(Point{ x: 10, y: 15 }));
         state.process(Message::Quit);