updated trove classifiers to include Python 3.7 and 3.8, and license (#653)

Author: beniwohli

setup.py

@@ -197,8 +197,11 @@ def run_tests(self):
         "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
         "Programming Language :: Python :: Implementation :: CPython",
         "Programming Language :: Python :: Implementation :: PyPy",
+        "License :: OSI Approved :: BSD License",
     ],
 )