setup.py: fix classifiers

setup.py

@@ -484,7 +484,9 @@ classifiers = """\
     Topic :: Scientific/Engineering
     Topic :: Scientific/Engineering :: Physics
     Operating System :: POSIX
-    Operating System :: Unix"""
+    Operating System :: Unix
+    Operating System :: MacOS :: MacOS X
+    Operating System :: Microsoft :: Windows"""
 
 
 def main():
@@ -502,7 +504,7 @@ def main():
                     'sdist': tkwant_sdist,
                     'build_ext': tkwant_build_ext},
           ext_modules=ext_modules(extensions()),
-          classifiers=classifiers,
+          classifiers=[c.strip() for c in classifiers.split('\n')],
           install_requires=requirements,
           tests_require=test_requirements,
           setup_requires=setup_requirements