correct supported operating systems

Author: Cube707

setup.py

@@ -52,7 +52,7 @@ def run_tests(self):
         "Environment :: Console",
         "Intended Audience :: Developers",
         "License :: OSI Approved :: MIT License",
-        "Operating System :: OS Independent",
+        "Operating System :: POSIX :: Linux",
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",