corrected os list in setup.py

Author: mbdevpl

setup.py

@@ -17,7 +17,9 @@ class Package(setup_boilerplate.Package):
         'Intended Audience :: Science/Research',
         'License :: OSI Approved :: Apache Software License',
         'Natural Language :: English',
-        'Operating System :: POSIX',
+        'Operating System :: MacOS :: MacOS X',
+        'Operating System :: Microsoft :: Windows',
+        'Operating System :: POSIX :: Linux',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3 :: Only',