Update README.md

Update the bibtex of the second publication from arXiv to RAL

README.md

@@ -18,13 +18,15 @@ These environments include (and evaluate) symbolic safety constraints and implem
 To reproduce the results in the article, see [branch `ar`](https://github.com/utiasDSL/safe-control-gym/tree/ar).
 
 ```bibtex
-@misc{yuan2021safecontrolgym,
-      title={safe-control-gym: a Unified Benchmark Suite for Safe Learning-based Control and Reinforcement Learning},
-      author={Zhaocong Yuan and Adam W. Hall and Siqi Zhou and Lukas Brunke and Melissa Greeff and Jacopo Panerati and Angela P. Schoellig},
-      year={2021},
-      eprint={2109.06325},
-      archivePrefix={arXiv},
-      primaryClass={cs.RO}}
+@article{yuan2021safecontrolgym,
+  author={Yuan, Zhaocong and Hall, Adam W. and Zhou, Siqi and Brunke, Lukas and Greeff, Melissa and Panerati, Jacopo and Schoellig, Angela P.},
+  journal={IEEE Robotics and Automation Letters}, 
+  title={Safe-Control-Gym: A Unified Benchmark Suite for Safe Learning-Based Control and Reinforcement Learning in Robotics}, 
+  year={2022},
+  volume={7},
+  number={4},
+  pages={11142-11149},
+  doi={10.1109/LRA.2022.3196132}}
 ```
 
 To reproduce the results in the article, see [branch `submission`](https://github.com/utiasDSL/safe-control-gym/tree/submission).