Add classifiers for Python 3.7 and 3.8

Author: Hugo Osvaldo Barrera

setup.py

@@ -89,6 +89,8 @@ def run(self):
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Topic :: Internet',
         'Topic :: Utilities',
     ],