Update README.md

README.md

@@ -68,10 +68,12 @@ PettingZoo keeps strict versioning for reproducibility reasons. All environments
 To cite this project in publication, please use
 
 ```
-@article{terry2020pettingzoo,
-  Title = {PettingZoo: Gym for Multi-Agent Reinforcement Learning},
-  Author = {Terry, J. K and Black, Benjamin and Grammel, Nathaniel and Jayakumar, Mario and Hari, Ananth and Sulivan, Ryan and Santos, Luis and Perez, Rodrigo and Horsch, Caroline and Dieffendahl, Clemens and Williams, Niall L and Lokesh, Yashas and Sullivan, Ryan and Ravi, Praveen},
-  journal={arXiv preprint arXiv:2009.14471},
-  year={2020}
+@article{terry2021pettingzoo,
+  title={Pettingzoo: Gym for multi-agent reinforcement learning},
+  author={Terry, J and Black, Benjamin and Grammel, Nathaniel and Jayakumar, Mario and Hari, Ananth and Sullivan, Ryan and Santos, Luis S and Dieffendahl, Clemens and Horsch, Caroline and Perez-Vicente, Rodrigo and others},
+  journal={Advances in Neural Information Processing Systems},
+  volume={34},
+  pages={15032--15043},
+  year={2021}
 }
 ```