"You are connecting to Redis v3.2.9, Sidekiq requires Redis v4.0.0 or greater?"

I recently updated Sidekiq in my Gemfile:

gem 'sidekiq', '~> 6.0', '>= 6.0.4'
gem 'redis', '~> 4.1', '>= 4.1.3'

But ever since updating, I get this error when running sidekiq in Terminal:

You are connecting to Redis v3.2.9, Sidekiq requires Redis v4.0.0 or greater.

I made sure to uninstall old versions of both Sidekiq and Redis, but Sidekiq is still trying to connect to 3.2.9. My Gemfile.lock has:

sidekiq (6.0.4)
  connection_pool (>= 2.2.2)
  rack (>= 2.0.0)
  rack-protection (>= 2.0.0)
  redis (>= 4.1.0)

Am I misreading this error? How would I tell Sidekiq to use the correct version of Redis?