Update app.py

app.py

@@ -25,7 +25,7 @@ def replay(model_id, filename, environment, evaluate):
 	model= PPO.load(checkpoint, custom_objects=custom_objects)
 
 	eval_env = make_atari_env(environment, n_envs=1)
-	eval_env = VecFrameStack(env, n_stack=4)
+	eval_env = VecFrameStack(eval_env, n_stack=4)
 
 	video_folder = 'logs/videos/'
 	video_length = 100