setup.py should support Python 2 to show a proper error message.

[ueshin]

No description provided.

[codecov-io]

Codecov Report

Merging #1027 into master will decrease coverage by 1.44%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1027      +/-   ##
==========================================
- Coverage   94.92%   93.47%   -1.45%     
==========================================
  Files          34       34              
  Lines        6699     6699              
==========================================
- Hits         6359     6262      -97     
- Misses        340      437      +97

Impacted Files	Coverage Δ
databricks/koalas/usage_logging/__init__.py	24.54% <0%> (-72.73%)	⬇️
databricks/koalas/usage_logging/usage_logger.py	50% <0%> (-50%)	⬇️
databricks/koalas/__init__.py	80.85% <0%> (-6.39%)	⬇️
databricks/conftest.py	94% <0%> (-4%)	⬇️

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[ueshin]

Thanks! I'd merge this now.