add Python 3.8 to setup.py

Author: skvark

setup.py

@@ -202,6 +202,7 @@ def main():
           'Programming Language :: Python :: 3.5',
           'Programming Language :: Python :: 3.6',
           'Programming Language :: Python :: 3.7',
+          'Programming Language :: Python :: 3.8',
           'Programming Language :: C++',
           'Programming Language :: Python :: Implementation :: CPython',
           'Topic :: Scientific/Engineering',