bumped pettingzoo version to 1.9.0

Merge pull request Farama-Foundation#377 from PettingZoo-Team/multiwa…

…lker_bugfix

Fixed multiwalker crashing on completion issue

bumped version to 1.8.1

bumped pettingzoo to 1.8.0

bumped pettingzoo to 1.7.0

bumped pettingzoo to 1.7.0

Merge pull request Farama-Foundation#348 from PettingZoo-Team/atari_c…

…lone_state

added gym style clone state methods to atari

bumped pettingzoo version to 1.6.0

bumped pettingzoo version to 1.5.2