dropbox in duplicity 0.8.13 (snap)

Hello,

I installed 0.8.13 with snap install duplicity --classic.

dropbox module fails with

File "/snap/duplicity/94/lib/python3.6/site-packages/dropbox/stone_serializers.py", line 665, in decode_union
  return data_type.definition(six.ensure_str(tag), val)
AttributeError: module 'six' has no attribute 'ensure_str'

dropbox 10.1.1 requires six >= 1.12.0