Pin jsonpickle. See whole-tale/girder_wholetale#447

[Xarthisius]

"Fixes" issue seen on stage deployment:

[2021-03-21 19:09:01,870: INFO/ForkPoolWorker-4] Successfully built image registry.stage.wholetale.org/605792f48b171335abe6d3d2/1616352419@sha256:25ce82fdb6a492f91c6f08e682b30b5ad9df0015ffcd3d9d79bd1f5ed45d123d
[2021-03-21 19:09:02,036: WARNING/ForkPoolWorker-4] /usr/local/lib/python3.8/dist-packages/celery/app/trace.py:622: RuntimeWarning: Exception raised outside body: AttributeError("'dict' object has no attribute 'apply_async'"):
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/dist-packages/kombu/utils/objects.py", line 42, in __get__
    return obj.__dict__[self.__name__]
KeyError: '_apply_async'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/dist-packages/celery/app/trace.py", line 474, in trace_task
    _chsig.apply_async(
  File "/usr/local/lib/python3.8/dist-packages/celery/canvas.py", line 224, in apply_async
    _apply = self._apply_async
  File "/usr/local/lib/python3.8/dist-packages/kombu/utils/objects.py", line 44, in __get__
    value = obj.__dict__[self.__name__] = self.__get(obj)
  File "/usr/local/lib/python3.8/dist-packages/celery/canvas.py", line 516, in _apply_async
    return self.type.apply_async
AttributeError: 'dict' object has no attribute 'apply_async'

[codecov]

Codecov Report

Merging #137 (310b562) into master (36ddf9e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #137   +/-   ##
=======================================
  Coverage   62.36%   62.36%           
=======================================
  Files           9        9           
  Lines        1225     1225           
=======================================
  Hits          764      764           
  Misses        461      461           

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[Xarthisius]

@craig-willis Since it's a trivial change, I'm gonna merge it so that a new image is built and waiting for you when you get back to this.