Show currently running job in qless worker procline

It looks like this may have been inadvertently removed in dc0684d. This
PR restores that behavior, albeit in a slightly different format.
Notably we omit the job state (since it must be running), and the job
data, which could be reasonably large.

lib/qless/worker/serial.rb

@@ -25,6 +25,7 @@ def run
           jobs.each do |job|
             # Run the job we're working on
             log(:debug, "Starting job #{job.klass_name} (#{job.jid} from #{job.queue_name})")
+            procline "Processing: #{job.jid} (#{job.klass_name}) from #{job.queue_name}"
             perform(job)
             log(:debug, "Finished job #{job.klass_name} (#{job.jid} from #{job.queue_name})")