Update redis exists

[arturictus]

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. (/home/artur/.asdf/installs/ruby/2.6.5/lib/ruby/gems/2.6.0/gems/sidekiq-6.0.7/lib/sidekiq/launcher.rb:160:in `block (2 levels) in ❤')