fix beta classifier

Author: jell-o-fishi

setup.cfg

@@ -13,7 +13,7 @@ long_description_content_type = text/markdown
 description = Python RSocket library
 zip_safe = True
 classifiers =
-    Development Status :: 3 - Beta
+    Development Status :: 4 - Beta
     Programming Language :: Python
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9