Description

Your current README says you do not support Python 3 and your trove classifiers for what versions of Python you support are non existent in your package metadata on PyPI. (https://pypi.python.org/pypi/slackclient)

Use this issue to track adding modern Python (>= 3.5+) support or documenting it if you already do. While you're at it, please add trove classifiers to your package to make the versions it supports clear in an automated fashion.

Programming Language :: Python :: 2.7
Programming Language :: Python :: 2 :: Only

thanks!