Add Python 3.8 to trove classifiers

Author: tony

setup.py

@@ -55,6 +55,7 @@
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: Implementation :: PyPy',
         "Topic :: Utilities",
         "Topic :: System :: Shells",