Correct download URL

Author: rocky

setup.py

@@ -252,7 +252,7 @@ def subdirs(root, file="*.*", depth=10):
     description="A general-purpose computer algebra system.",
     license="GPL",
     url="https://mathics.org/",
-    download_url="https://github.com/Mathics/mathics-core/releases",
+    download_url="https://github.com/Mathics3/mathics-core/releases",
     keywords=["Mathematica", "Wolfram", "Interpreter", "Shell", "Math", "CAS"],
     classifiers=[
         "Intended Audience :: Developers",