Sidekiq::MemoryKiller: Add missing space in log message

The sidekiq memory killer prints warnings like

gitlab-sidekiq[8245]: 2017-09-27T11:31:43.192Z 8245 TID-ov9l6b4e0 WARN:
this thread will shut down PID 8245 - Worker ProjectWebHookWorker -
JID-dd3b1c23a653deec5e575ab4in 900 seconds

There is a space missing between the JID and 'in'.