Add Trove classifier for Python 3.7

Author: webknjaz

setup.py

@@ -93,6 +93,7 @@ def read(f):
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
         'Development Status :: 5 - Production/Stable',
     ],
     author='Andrew Svetlov',