Finally… Solved.. I have downgraded sidekiq to 4.1.2
gem uninstall sidekiq
gem install sidekiq --version '<=4.1.2'
/home/carlos/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/bundler-1.12.5/lib/bundler/runtime.rb:35:in block in setup': You have already activated activesupport 5.0.0, but your Gemfile requires activesupport 4.2.7. Prepending bundle exec` to your command may solve this. (Gem::LoadError)
So bundle exec sidekiq works perfectly..