using six from pypi package for django3 compatibility

[snake-soft]

#255

[codecov]

Codecov Report

Merging #256 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #256   +/-   ##
=======================================
  Coverage   63.91%   63.91%           
=======================================
  Files          25       25           
  Lines        1294     1294           
=======================================
  Hits          827      827           
  Misses        467      467           

Impacted Files	Coverage Δ
paypal/express/models.py	96.15% <100.00%> (ø)
paypal/payflow/models.py	75.47% <100.00%> (ø)

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[solarissmoke]

We've dropped support for Python 2 - so I think it's better instead to drop all use of Python 2 compatible shims instead of using six.

[sasha0]

I agree.

[sasha0]

Alright, I already addressed that.

[solarissmoke]

Closing on the basis that Python 2 support will be dropped entirely in the next release.