Avoid redis-rb >= 4.2 due to exists API deprecation.

Author: mperham

sidekiq.gemspec

@@ -14,8 +14,8 @@ Gem::Specification.new do |gem|
   gem.version       = Sidekiq::VERSION
   gem.required_ruby_version = ">= 2.2.2"
 
-  gem.add_dependency 'redis', '>= 3.3.5', '< 5'
+  gem.add_dependency 'redis', '>= 3.3.5', '< 4.2'
   gem.add_dependency 'connection_pool', '~> 2.2', '>= 2.2.2'
-  gem.add_dependency 'rack', '< 2.2.0'
+  gem.add_dependency 'rack', '~> 2.0'
   gem.add_dependency 'rack-protection', '>= 1.5.0'
 end