CellUnion.expand() raises "AttributeError: 'CellId' object has no attribute 'append_all_neighbors'"

[osher-y]

Code to reproduce:

from s2sphere import *
cell_union = s2sphere.CellUnion([CellId.from_lat_lng(LatLng(0, 0))])
cell_union.expand(3)

Outputs the following:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-275-185a13c92e77> in <module>()
      1 from s2sphere import *
      2 cell_union = s2sphere.CellUnion([CellId.from_lat_lng(LatLng(0, 0))])
----> 3 cell_union.expand(3)

/usr/local/lib/python3.5/site-packages/s2sphere/sphere.py in expand(self, *args)
   2682                         i -= 1
   2683                 output.append(cell_id)
-> 2684                 cell_id.append_all_neighbors(level, output)
   2685                 i -= 1
   2686             self.__cell_ids = output

AttributeError: 'CellId' object has no attribute 'append_all_neighbors'

[nickadoodle777]

fixed the issue in 3. https://github.com/sidewalklabs/s2sphere/issues/37