Describe your feature request

When you try to combine latest ray and ray[tune] py packages from PyPI with the latest redis py package (also from PyPI) you get an error, caused by ray pinning its Redis dependency in a rather restrictive, non-future-proof way (with a rarely seen "less" inequality sign) blocking Redis from any future upgrades or patches.

pip error message:

ERROR: ray 0.8.5 has requirement redis<3.5.0,>=3.3.2, but you'll have redis 3.5.3 which is incompatible.