Update Sidekiq before Redis 5.0 launch

[cbaudouinjr]

Currently getting a warning in our logs that highlights a feature of Redis that is being removed in Redis 5.0

Redis#exists(key) will return an Integer in redis-rb 4.3. "exists?" returns a boolean, you should use it instead. To opt-in to the new behavior now you can set Redis.exists_returns_integer = true. To disable this message and keep the current (boolean) behaviour of "exists" you can set "Redis.exists_returns_integer = false", but this option will be removed in 5.0. (/app/vendor/bundle/ruby/2.6.0/gems/sidekiq-6.0.7/lib/sidekiq/launcher.rb:160:in "block (2 levels) in ❤")

[cbaudouinjr]

Blocked by #462. Also worth noting that while this does resolve a bulk of the warnings, we use a sidekick gem 😉 sidekiq-cron that still needs to be updated. See sidekiq-cron/sidekiq-cron#286