Add Python 3 only classifier
Python 2 support was removed during Ussuri cycle. This change adds
the classifier to clearly state that only Python 3 is supported.
@@ -14,6 +14,7 @@ classifier =
License :: OSI Approved :: Apache Software License
Operating System :: POSIX :: Linux
Programming Language :: Python
+ Programming Language :: Python :: 3 :: Only
Programming Language :: Python :: 3
Programming Language :: Python :: 3.6
Programming Language :: Python :: 3.7
