[DRE-maint] ruby-sidekiq-cron is marked for autoremoval from testing

[Debian testing autoremoval watch]

ruby-sidekiq-cron 0.4.2-5 is marked for autoremoval from testing on 2016-10-17

It (build-)depends on packages with these RC bugs:
836536: ruby-concurrent: FTBFS too much often (failed examples)