Update supported Redis

[thenewguy]

Per supported technology docs, redis client support is >=2.8,<3.2.0. Please revisit this as <3.2.0 means not updated since Janurary 2019 per https://pypi.org/project/redis/#history

[basepi]

Thanks for this. Looks like our CI is testing against lastest redis so I think we can just remove the upper limit on that doc. I'll submit a PR shortly.