DOC: more consistent flake8-commands in contributing.rst#23724

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jreback merged 5 commits intopandas-dev:masterfrom

h-vetinari:contrib_flake8

Nov 20, 2018

Commits on Nov 15, 2018

Commits on Nov 16, 2018

Commits on Nov 19, 2018

Also harmonize makefile lint-diff
h-vetinari
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