update operating system section

setup.py

@@ -56,9 +56,7 @@ setup(name=pwman.appname,
           'Intended Audience :: Developers',
           'Intended Audience :: System Administrators',
           'License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)',
-          'Operating System :: MacOS :: MacOS X',
-          'Operating System :: Microsoft :: Windows',
-          'Operating System :: POSIX',
+          'Operating System :: OS Independent',
           'Programming Language :: Python',
           'Programming Language :: Python :: 2.7'
       ],