Update classifier

Author: DanielBok

setup.cfg

@@ -18,7 +18,7 @@ keywords =
     optimization
     non-linear optimization
 classifiers =
-    Development Status :: 5 - Production
+    Development Status :: 5 - Production/Stable
     Intended Audience :: End Users/Desktop
     Intended Audience :: Education
     License :: OSI Approved :: MIT License