Out of date dependency: concurrent-ruby

[pboling]

https://github.com/ruby-concurrency/concurrent-ruby

v1.2.0 was released more than a year ago, and crurent is v1.2.3.

There are many fixes we need among those updates!

[elioncho]

This is incompatible with the latest version of solid_queue due to the concurrent-ruby dependency

[pubnub-release-bot]

@pboling this issue is addressed in v5.3.5