Update to fix test failures caused by update to pyyaml-5.1

[drdavella]

This resolves #659.

[stsci-bot]

Hi there @drdavella 👋 - thanks for the pull request! I'm just a friendly 🤖 that checks for issues related to the changelog. I help make sure that this pull request is milestoned and labeled correctly. This is mainly intended for the maintainers, so if you are not a maintainer you can ignore this, and a maintainer will let you know if any action is required on your part 😃.

Everything looks good from my point of view! 👍

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[codecov]

Codecov Report

Merging #662 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #662      +/-   ##
==========================================
+ Coverage   93.24%   93.24%   +<.01%     
==========================================
  Files          39       39              
  Lines        4292     4295       +3     
==========================================
+ Hits         4002     4005       +3     
  Misses        290      290

Impacted Files	Coverage Δ
asdf/yamlutil.py	97.91% <100%> (+0.04%)	⬆️

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