Recent release of emcee (3.0.0) does not work within BILBY

The recent update to emcee (to version 3.0.0) has broken its implementation within bilby. The traceback that appears when running a standard gaussian_example.py with emcee is:

Traceback (most recent call last):
  File "gaussian_example.py", line 53, in <module>
    nwalkers=10, outdir=outdir, label=label, store=True, thin=100, live_dangerously=True)
  File "/home/ethan/Research/code_libraries/bilby/bilby/core/sampler/__init__.py", line 175, in run_sampler
    result = sampler.run_sampler()
  File "/home/ethan/Research/code_libraries/bilby/bilby/core/sampler/emcee.py", line 345, in run_sampler
    iterations -= self._previous_iterations
  File "/home/ethan/Research/code_libraries/bilby/bilby/core/sampler/emcee.py", line 310, in _previous_iterations
    return len(self.sampler.blobs)
  File "/home/ethan/Research/dev3/lib/python3.6/site-packages/emcee/utils.py", line 26, in f
    return func(*args, **kwargs)
  File "/home/ethan/Research/dev3/lib/python3.6/site-packages/emcee/ensemble.py", line 491, in blobs
    return self.get_blobs()
  File "/home/ethan/Research/dev3/lib/python3.6/site-packages/emcee/ensemble.py", line 509, in get_blobs
    return self.get_value("blobs", **kwargs)
  File "/home/ethan/Research/dev3/lib/python3.6/site-packages/emcee/ensemble.py", line 524, in get_value
    return self.backend.get_value(name, **kwargs)
  File "/home/ethan/Research/dev3/lib/python3.6/site-packages/emcee/backends/backend.py", line 43, in get_value
    raise AttributeError("you must run the sampler with "
AttributeError: you must run the sampler with 'store == True' before accessing the results

@moritz.huebner @colm.talbot

Cheers Gavin Wallace for spotting this issue 😄