Does not run with more recent versions of dependencies #60

I have tried to run the test code from the README with the example dataset and get an error (TypeError: must be real number, not list) on the line:

iris_dabest.mean_diff.plot(), and occurs due to this line in the gapped_lines function:

--> 162 quantiles = data.groupby(x)[y].quantile([0.25, 0.75])
163 .unstack()
164 .reindex(index=group_order)

I am using Python3.7 with the following modules:

scipy 1.3.0
seaborn 0.9.0
pandas 0.25.0
numpy 1.17.0
matplotlib 3.1.1

which I notice are more recent versions of the dependencies. I installed dabest using pip. I have also built the cloned version to test and get the same error.

I have forked a copy of the code to see if there is a simple fix.