tests.py failure: no attribute 'exponential_time'

Hi Greg, returning to PyFstat after a while. With 5837254c the examples still seem to work, but tests.py throws the following:

12:30 INFO    : The config file TestData/Test.cff has been modified since the sft file TestData/H-4800_H1_1800SFT_Test-700000000-8640000.sft was created
12:30 INFO    : Now executing: lalapps_Makefakedata_v5 --outSingleSFT=TRUE --outSFTdir="TestData" --outLabel="Test" --IFOs="H1" --sqrtSX="1" --startTime=700000000 --duration=8640000 --fmin=28 --Band=4 --Tsft=1800 --injectionSources="TestData/Test.cff"
.
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ERROR: test_fully_coherent (__main__.TestMCMCSearch)
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Traceback (most recent call last):
  File "tests.py", line 227, in test_fully_coherent
    search.run(create_plots=False)
  File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 433, in run
    sampler = self._run_sampler(sampler, p0, nburn=nburn, nprod=nprod)
  File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 345, in _run_sampler
    self._run_sampler_with_conv_test(sampler, p0, nprod, nburn)
  File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 326, in _run_sampler_with_conv_test
    **self.convergence_kwargs):
  File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 316, in _test_convergence
    return self._get_convergence_test(i, sampler, **kwargs)
  File "/home/dkeitel/git/PyFstat/pyfstat/mcmc_based_searches.py", line 282, in test_autocorr_convergence
    acors[temp, :] = emcee.autocorr.exponential_time(x)
AttributeError: 'module' object has no attribute 'exponential_time'

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Ran 11 tests in 142.569s

FAILED (errors=1)