Update semaphore redis to initialize a new conn

The redis-semaphore gem advises [against reusing the redis connection across threads](dv/redis-semaphore#18) because it causes a Deadlock. We actually experience this and the solution was to initialize a new redis connection when checking for the semaphore.

I additionally added a staleness check to avoid locking everything forever should the semaphore hang for some other reason.

lib/sidekiq-rate-limiter/fetch.rb

@@ -32,7 +32,7 @@ def limit(work)
  }
 
  Sidekiq.redis do |conn|
- s = Redis::Semaphore.new(:sidekiq_rate_limit_exceeded_check, redis: conn)
+ s = Redis::Semaphore.new(:sidekiq_rate_limit_exceeded_check, redis: Sidekiq::RedisConnection.create, stale_client_timeout: 60)
  lim = Limit.new(conn, options)
  limit_exceeded = nil