chore: Bump jsdom to 15

[eps1lon]

Not sure which version we should use. While the latest is 16 it isn't the default version used in jest. Ideally we would test with jsdom 15 and 16 just to be aware of changes between those versions.

What:

Bump used jsdom version to 15.2.1

Why:

jsdom 15 has MutationObserver support as well as perf improvements.

How:

• fixing breaking changes in jest and jsodm

Checklist:

• Documentation added to the
  docs site
• I've prepared a PR for types targeting
  DefinitelyTyped
• Tests
• Ready to be merged
  

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[eps1lon]

Fixes

Jest: Multiple inline snapshots for the same call are not supported.

[codecov]

Codecov Report

Merging #447 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #447   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          22     22           
  Lines         385    385           
  Branches       91     91           
=====================================
  Hits          385    385

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[kentcdodds]

Looks like the snapshots are pretty much useless now. We'll need these tests to be rewritten to make sure they're testing what they should be. Maybe by making more explicit assertions on the mutation record.

[eps1lon]

@kentcdodds Will do. I didn't look closely what the purpose of the test was.

Should we leverage custom snapshot serializers or serialize them directly in the test?

[kentcdodds]

👍 thanks!

[kentcdodds]

🎉 This PR is included in version 6.13.0 🎉

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• GitHub release

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