Include Python 3.8 in classifier

Author: nicoddemus

setup.py

@@ -170,6 +170,7 @@ def read(*parts):
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Topic :: Software Development :: Testing',
         'Topic :: Software Development :: Libraries :: Python Modules',
     ],