BLD Remove Python 3.6 compatibility.

Author: twiecki

setup.py

@@ -21,7 +21,6 @@
                'Programming Language :: Python :: 2.7',
                'Programming Language :: Python :: 3.4',
                'Programming Language :: Python :: 3.5',
-               'Programming Language :: Python :: 3.6',
                'License :: OSI Approved :: Apache Software License',
                'Intended Audience :: Science/Research',
                'Topic :: Scientific/Engineering',