Support Rails 8

[kmcphillips]

Specifying a < 8 for actionpack(rails) means that this gem is incompatible with Rails 8 for now.

The real problem here is that 0.7.0 had no dependency versions defined so any app attempting to upgrade without specifying a min version of this gem will get downgraded to 0.7.0:
https://github.com/roidrage/redis-session-store/blob/v0.7.0/redis-session-store.gemspec#L21

That causes this exception for us at runtime:

/redis-session-store-0.7.0/lib/redis-session-store.rb:10:in `<class:RedisSessionStore>': uninitialized constant Rack::Session::Abstract::ENV_SESSION_OPTIONS_KEY (NameError)

    ENV_SESSION_OPTIONS_KEY = Rack::Session::Abstract::ENV_SESSION_OPTIONS_KEY

This was similarly encountered for Rails 6 in #110

[kmcphillips]

Ping @Jesterovskiy

[Jesterovskiy]

Thanks for your contribution! Right now, I don't have time to support this repo at all =(

[kmcphillips]

That's ok. @Jesterovskiy, it's pretty legacy anyway. I think you can just use the built in ActionDispatch::Session::CacheStore with a redis cache and get nearly the same thing.

I'm just trying to minimally unblock people who already depend on it.

I'll open a PR with the version bump, then can you just release it?

[kmcphillips]

#152