setup: Add trove classifier for Python 3.6.

Author: htgoebel

setup.py

@@ -72,6 +72,7 @@ def read(filename):
 Programming Language :: Python :: 3.4
 Programming Language :: Python :: 3.5
 Programming Language :: Python :: 3.6
+Programming Language :: Python :: 3.7
 Programming Language :: Python :: Implementation :: CPython
 Topic :: Software Development
 Topic :: Software Development :: Build Tools