examples: use app.gg.quit() instead of exit(0)

examples/2048/2048.v

@@ -788,7 +788,7 @@ fn (mut app App) on_key_down(key gg.KeyCode) {
 	// these keys are independent from the game state:
 	match key {
 		.a { app.is_ai_mode = !app.is_ai_mode }
-		.escape { exit(0) }
+		.escape { app.gg.quit() }
 		.n, .r { app.new_game() }
 		.backspace { app.undo() }
 		.enter { app.next_tile_format() }

examples/flappylearning/game.v

@@ -274,7 +274,7 @@ fn (mut app App) key_down(key gg.KeyCode) {
 	// global keys
 	match key {
 		.escape {
-			exit(0)
+			app.gg.quit()
 		}
 		._0 {
 			app.timer_period_ms = 0

examples/tetris/tetris.v

@@ -459,7 +459,7 @@ fn (mut game Game) key_down(key gg.KeyCode) {
 	// global keys
 	match key {
 		.escape {
-			exit(0)
+			game.gg.quit()
 		}
 		.space {
 			if game.state == .running {