Add Python 3.8 to classifiers (#406)

Author: tkf

setup.py

@@ -66,6 +66,7 @@ def pyload(path):
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
       ],
       url='http://julialang.org',
       project_urls={