Removed invalid classifier identified by PyPI.

Author: victor73

setup.py

@@ -21,7 +21,6 @@ def read(fname):
         "Intended Audience :: Science/Research",
         "Natural Language :: English",
         "Operating System :: POSIX",
-        "Operating System :: UNIX",
         "Programming Language :: Python :: 2.7",
         "Topic :: Utilities",
         "Topic :: Scientific/Engineering",