Make use of zig switch syntax

src/main.zig

@@ -49,8 +49,8 @@ pub fn main() !void {
         _ = SDL.SDL_RenderClear(renderer);
 
         current_state = switch (current_state) {
-            State.main_menu => main_menu.tick(),
-            State.game => game.tick(),
+            .main_menu => main_menu.tick(),
+            .game => game.tick(),
         };
 
         SDL.SDL_RenderPresent(renderer);