Bump redis dependency version to < 5

[jsantos]

Fixes #18

• https://github.com/redis/redis-rb/blob/master/CHANGELOG.md#401
• Also sorted dependencies alphabetically, as per Rubocop's suggestion

[jsantos]

@Onumis Are you familiar with the release process here? Shall I include a version bump in order to release the update to Rubygems? \cc @adbjesus

[nunosilva800]

@jsantos yes a version bump and release to rubygems. but @adbjesus needs to set you as a gem maintainer on rubygems.

Alternatively, you can use this via github, on Gemfile:

gem 'sidekiq-worker_stats',
    github: 'whitesmith/sidekiq-worker_stats',
    ref: '2e0fbe8d80318ed8d036e5f109c3ec4294e55115'

[jsantos]

@Onumis Yup, I can always use the direct github reference, just didn't wanted the version on Rubygems to fall too much behind. LGTM