Does not work on older versions of Redis

[AKhoo]

sidekiq-grouping does not appear to work for older versions of Redis.

Specifically, one issue I am experiencing is that Redis versions <6.2 don't have the count argument available in lpop, which causes the PLUCK_SCRIPT used by Sidekiq::Grouping::Redis#pluck to result in the following error message:

Redis::CommandError: ERR Error running script (call to f_717b4b61a9929bb9dffcebe0a6697c98b90f6b11): @user_script:1: @user_script: 1: Wrong number of args calling Redis command From Lua script
from /Users/user_name/.rvm/gems/ruby-2.7.3/gems/redis-4.4.0/lib/redis/client.rb:149:in `call'

[russointroitoa]

Hey @AKhoo The issue should be fixed by #58