title: redis / rq worker breaking on python3
body: <p>So I am getting error while executing code in rq worker </p>
  
  <pre><code> File "/usr/local/bin/rq", line 11, in &lt;module&gt;
     sys.exit(main())
   File "/usr/local/lib/python3.7/site-packages/click/core.py", line 764, in __call__
     return self.main(*args, **kwargs)
   File "/usr/local/lib/python3.7/site-packages/click/core.py", line 717, in main
     rv = self.invoke(ctx)
   File "/usr/local/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
     return _process_result(sub_ctx.command.invoke(sub_ctx))
   File "/usr/local/lib/python3.7/site-packages/click/core.py", line 956, in invoke
     return ctx.invoke(self.callback, **ctx.params)
   File "/usr/local/lib/python3.7/site-packages/click/core.py", line 555, in invoke
     return callback(*args, **kwargs)
   File "/usr/local/lib/python3.7/site-packages/rq/cli/cli.py", line 75, in wrapper
     return ctx.invoke(func, cli_config, *args[1:], **kwargs)
   File "/usr/local/lib/python3.7/site-packages/click/core.py", line 555, in invoke
     return callback(*args, **kwargs)
   File "/usr/local/lib/python3.7/site-packages/rq/cli/cli.py", line 236, in worker
     worker.work(burst=burst, logging_level=logging_level)
   File "/usr/local/lib/python3.7/site-packages/rq/worker.py", line 493, in work
     self.execute_job(job, queue)
   File "/usr/local/lib/python3.7/site-packages/rq/worker.py", line 662, in execute_job
     self.fork_work_horse(job, queue)
   File "/usr/local/lib/python3.7/site-packages/rq/worker.py", line 599, in fork_work_horse
     self.main_work_horse(job, queue)
   File "/usr/local/lib/python3.7/site-packages/rq/worker.py", line 677, in main_work_horse
     success = self.perform_job(job, queue)
   File "/usr/local/lib/python3.7/site-packages/rq/worker.py", line 781, in perform_job
     self.prepare_job_execution(job)
   File "/usr/local/lib/python3.7/site-packages/rq/worker.py", line 706, in prepare_job_execution
     registry.add(job, timeout, pipeline=pipeline)
   File "/usr/local/lib/python3.7/site-packages/rq/registry.py", line 47, in add
     return pipeline.zadd(self.key, score, job.id)
   File "/usr/local/lib/python3.7/site-packages/redis/client.py", line 2263, in zadd
     for pair in iteritems(mapping):
   File "/usr/local/lib/python3.7/site-packages/redis/_compat.py", line 123, in iteritems
  return iter(x.items())
  
  AttributeError: 'int' object has no attribute 'items'
  14:04:29 Moving job to 'failed' queue (work-horse terminated unexpectedly; waitpid returned 256)
  </code></pre>
  
  <p>I am trying to run this code in decoupled containers on openshift. Same images work locally. I guess only difference is I was running rq worker on system instead on container when trying locally and my local have both python 2 and 3 while openshift have python3 only. </p>
  
  <p>Can anyone resolve why it started behaving like this. I suspect its due to python version. but i dont know how to run <code>redis/ rq worker</code> with python 2.</p>