Update setup.py classifier (Beta -> Stable) (#1508)

Summary:
Pull Request resolved: #1508

Update classifier in line with the README Beta text removal.

Reviewed By: sarahtranfb

Differential Revision: D69953558

fbshipit-source-id: 8eb6981d3f0057ff2c7056ce82d9398c5a1ecb6e

Author: craymichael

setup.py

@@ -142,7 +142,7 @@ def get_package_files(root, subdirs):
             "PyTorch",
         ],
         classifiers=[
-            "Development Status :: 4 - Beta",
+            "Development Status :: 5 - Production/Stable",
             "Intended Audience :: Developers",
             "Intended Audience :: Education",
             "Intended Audience :: Science/Research",