chore: add info about support Python 3.8

Author: bednar

setup.py

@@ -44,6 +44,7 @@
         'License :: OSI Approved :: MIT License',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Topic :: Database',
         'Topic :: Software Development :: Libraries',
         'Topic :: Software Development :: Libraries :: Python Modules',