chore(deps): update pyyaml requirement from ~=4.2b1 to ~=5.1

[dependabot-preview]

Updates the requirements on pyyaml to permit the latest version.

Changelog

Sourced from pyyaml's changelog.

5.1 (2019-03-13)

• #35 -- Some modernization of the test running
• #42 -- Install tox in a virtualenv
• #45 -- Allow colon in a plain scalar in a flow context
• #48 -- Fix typos
• #55 -- Improve RepresenterError creation
• #59 -- Resolves #57, update readme issues link
• #60 -- Document and test Python 3.6 support
• #61 -- Use Travis CI built in pip cache support
• #62 -- Remove tox workaround for Travis CI
• #63 -- Adding support to Unicode characters over codepoint 0xffff
• #65 -- Support unicode literals over codepoint 0xffff
• #75 -- add 3.12 changelog
• #76 -- Fallback to Pure Python if Compilation fails
• #84 -- Drop unsupported Python 3.3
• #102 -- Include license file in the generated wheel package
• #105 -- Removed Python 2.6 & 3.3 support
• #111 -- Remove commented out Psyco code
• #129 -- Remove call to ord in lib3 emitter code
• #143 -- Allow to turn off sorting keys in Dumper
• #149 -- Test on Python 3.7-dev
• #158 -- Support escaped slash in double quotes "/"
• #181 -- Import Hashable from collections.abc
• #256 -- Make default_flow_style=False
• #257 -- Deprecate yaml.load and add FullLoader and UnsafeLoader classes
• #263 -- Windows Appveyor build

3.13 (2018-07-05)

• Resolved issues around PyYAML working in Python 3.7.

3.12 (2016-08-28)

• Wheel packages for Windows binaries.
• Adding an implicit resolver to a derived loader should not affect the base loader.
• Uniform representation for OrderedDict? across different versions of Python.
• Fixed comparison to None warning.

3.11 (2014-03-26)

• Source and binary distributions are rebuilt against the latest
  versions of Cython and LibYAML.

3.10 (2011-05-30)

... (truncated)

Commits

• e471e86 Updates for 5.1 release
• 9141e90 Windows Appveyor build
• d6cbff6 Skip certain unicode tests when maxunicode not > 0xffff
• 69103ba Update .travis.yml to use libyaml 0.2.2
• 91c9435 Squash/merge pull request #105 from nnadeau/patch-1
• 507a464 Make default_flow_style=False
• 07c88c6 Allow to turn off sorting keys in Dumper
• 611ba39 Include license file in the generated wheel package
• 857dff1 Apply FullLoader/UnsafeLoader changes to lib3
• 0cedb2a Deprecate/warn usage of yaml.load(input)
• Additional commits viewable in compare view

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[codecov]

Codecov Report

Merging #5920 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development    #5920   +/-   ##
============================================
  Coverage        66.51%   66.51%           
============================================
  Files              286      286           
  Lines            13925    13925           
============================================
  Hits              9262     9262           
  Misses            4663     4663

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