Change minimum required pandas version to 0.21.0

[martinholmer]

This pull request increases from 0.20.1 to 0.21.0 the minimum required version of pandas.

This change is required for the new reforms test (see revisions in the test_reform_json_and_output function that are part of pull request #1766), which use the mapper argument of the pandas.rename method that was first added in pandas version 0.21. Thanks to @derrickchoe, who was using an older version of pandas, for pointing this out.

The unit tests will fail unless you upgrade using this command: conda update pandas

[codecov-io]

Codecov Report

Merging #1781 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1781   +/-   ##
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  Coverage     100%    100%           
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  Files          37      37           
  Lines        3028    3028           
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  Hits         3028    3028

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[derrickchoe]

@martinholmer

Thanks for letting me know-- I've updated my version of pandas.

Edit:

I've re-run the tests, and the only current issues are with test_pufcsv.py and test_puf_var_stats.py

I appreciate your identifying the issue with my pandas version so quickly!