Merge branch 'cs-upgrade-redis-actionpack' into 'master'

Upgrade redis-rails from 4.0.0 to 5.0.1.

This updates redis-rails to 5.0.1 along with its dependencies. I helped upgrade redis-actionpack so it would work with both Rails 4.2 and 5.0 in the same version.

Unfortunately none of the gems have Changelogs :/

- redis-rails: https://github.com/redis-store/redis-rails
- redis-actionpack: https://github.com/redis-store/redis-actionpack
- redis-activesupport: https://github.com/redis-store/redis-activesupport
- redis-rack: https://github.com/redis-store/redis-rack
- redis-store: https://github.com/redis-store/redis-store

Working toward #14286.

See merge request !7291