TypeError: set_agent_id() missing 1 required positional argument: 'agent_id'

[ZiyiLiubird]

When I try to reproduce the example in (https://tianshou.readthedocs.io/en/master/tutorials/tictactoe.html), I encounter an type error: TypeError: object of type 'PettingZooEnv' has no len()
The complete error information is as follows:

Traceback (most recent call last):
  File "tic_tac_toe.py", line 244, in <module>
    watch(args, agent)
  File "tic_tac_toe.py", line 236, in watch
    collector = Collector(policy, env, exploration_noise=True)
  File "/home/lzy/miniconda3/envs/ray/lib/python3.8/site-packages/tianshou/data/collector.py", line 70, in __init__
    self.env_num = len(self.env)
TypeError: object of type 'PettingZooEnv' has no len()

Writing "env = DummyVectorEnv([lambda:env])" after "env = get_env()" can fix this error. Maybe the tutorials should be updated?

[Trinkle23897]

Thanks for reporting this issue! Yes, feel free to open a pull request to update the tutorial.