deps: update peerDeps to support React 17 without warnings

[agilgur5]

Summary

Update peerDependencies range to support React 17

Fixes #58 Closes #64

Description

• seems to work without any component modifications needed on React 17

  • it was supposed to have "no new features" in any case per the release blog post
  • https://reactjs.org/blog/2020/10/20/react-v17.html

• ensure tests pass with React 17

  • update devDeps to React 17 + react-dom 17
  • update devDeps to use unofficial Enzyme Adapter for React 17
  • official adapter has yet to be released, but this seems to work for many people and the usage here is quite simple, so should be fine for this use-case
    • and tests seem to pass without issue too
    • React 18 will be a separate story, but will cross that bridge when we get there
    • see more details in https://github.com/agilgur5/react-signature-canvas/pull/64#pullrequestreview-876834510

Review Notes

Had to do some manual things in the background like migrating and re-setting-up Travis (and emailing them about OSS credits etc) as well as making sure Codecov still works etc. Make sure everything passes here before merging!

Will PR and merge my old standardization branch after this just to have less changes for this (less things to break). Those commits are like 2 years old now but still relevant. Will see about #42 after

[codecov[bot]]

Codecov Report

Merging #69 (13436f7) into main (d449c18) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##              main       #69   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines           59        59           
  Branches         6         6           
=========================================
  Hits            59        59           

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