Allow react 17 as peerDependency

[anajavi]

Adds react 17 as peerDependency to prevent warnings.

Description

Allows react 17 as peerDependency
fixes #792
fixes #774

Motivation and Context

react-datetime works with react 17.

Testing against react 17 is blocked by enzyme-adapter-17, which still in development: enzymejs/enzyme#2430

Checklist

[X] I have not included any built dist files (us maintainers do that prior to a new release)
[ ] I have added tests covering my changes
[X] All new and existing tests pass
[ ] My changes required the documentation to be updated
  [ ] I have updated the documentation accordingly
  [ ] I have updated the TypeScript 1.8 type definitions accordingly
  [ ] I have updated the TypeScript 2.0+ type definitions accordingly

[zackdotcomputer]

Resolves #774

[tamal-appsbee]

Please merge it.

[dmathijs]

Why does this remain open?

[zackdotcomputer]

@arqex hasn't been very active on Github since last fall and IDK if anyone else has merge rights on the repo.

[arqex]

Thanks @anajavi for sending the change and @layneanderson for merging it! I've just published the v3.1.0 with react 17 as peer dependency.