Require redis >=4.2,<4.6

[lqmanh]

Resolve #63

[tobymao]

this is not correct because redis broke cancel catching in 4.4 look at

redis/redis-py#2104

[tobymao]

this is still open redis/redis-py#2511

[lqmanh]

Okay this seems really bad. Guess I have to find some workaround then :(((
Thanks for your quick response 👍🏼

[kartzke]

Looks like this PR may fix the issue: redis/redis-py#2695

It's been hanging for 3 months. There's been some dialog in the last few days, but it needs the attention of a redis-py maintainer.