loading a dicom series generates TypeError

[satra]

just noting this here for now.

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-20-13b4a533131d> in <module>()
----> 1 nibabel.nicom.dicomreaders.slices_to_series([nibabel.nicom.dicomreaders.wrapper_from_file(val) for val in fl])

/software/miniconda3/envs/dev36pype/lib/python3.6/site-packages/nibabel/nicom/dicomreaders.py in slices_to_series(wrappers)
    147     for vol_list in volume_lists:
    148         if len(vol_list) > 1:
--> 149             vol_list.sort(_slice_sorter)
    150             zs = [s.slice_indicator for s in vol_list]
    151             if len(set(zs)) < len(zs):  # not unique zs

TypeError: must use keyword argument for key function

[effigies]

Fixed in #728.