typo fix (pandas-dev#41642)

Author: iynehz

setup.cfg

@@ -14,7 +14,7 @@ classifiers =
     Environment :: Console
     Intended Audience :: Science/Research
     License :: OSI Approved :: BSD License
-    Operating System :: OS Independen
+    Operating System :: OS Independent
     Programming Language :: Cython
     Programming Language :: Python
     Programming Language :: Python :: 3