Fix author e-mail

Author: jank324

setup.py

@@ -5,7 +5,7 @@
     name="cheetah",
     version="0.5.13",
     author="Jan Kaiser & Oliver Stein",
-    author_email="[email protected] | [email protected]",
+    author_email="[email protected]",
     description="Fast particle accelerator optics simulation for reinforcement learning and optimisation applications.",
     url="https://github.com/desy-ml/cheetah",
     packages=["cheetah"],