updates to release version 3.9.1

[raleigh-g-thompson]

bumps version to 3.9.1 in preparation for release

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 19.76%. Comparing base (111bda0) to head (cae5ac6).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #576   +/-   ##
=========================================
  Coverage     19.76%   19.76%           
  Complexity     1644     1644           
=========================================
  Files           310      310           
  Lines         27283    27283           
  Branches       4317     4317           
=========================================
  Hits           5393     5393           
  Misses        20997    20997           
  Partials        893      893           

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