chore(requirements): update requests to 2.13.0

[mboersma]

From the requests library release notes:

Features

• Only load the idna library when we've determined we need it. This will save some memory for users.

Miscellaneous

• Updated bundled urllib3 to 1.20.
• Updated bundled idna to 2.2.

[codecov-io]

Codecov Report

Merging #1235 into master will not impact coverage.

@@           Coverage Diff           @@
##           master    #1235   +/-   ##
=======================================
  Coverage   87.29%   87.29%           
=======================================
  Files          43       43           
  Lines        3826     3826           
  Branches      665      665           
=======================================
  Hits         3340     3340           
  Misses        321      321           
  Partials      165      165

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[mboersma]

This actually breaks a regex-based unit test, so I'll work that out and then resubmit it for review.

[mboersma]

My rewriting of import statements somehow had caused the unit test failure, so I reverted that. Works fine now: ready for review again.