fix(deps): update dependency is-plain-obj to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
is-plain-obj	^3.0.0 -> ^4.0.0

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Release Notes

sindresorhus/is-plain-obj

### [`v4.0.0`](https://togithub.com/sindresorhus/is-plain-obj/releases/v4.0.0) [Compare Source](https://togithub.com/sindresorhus/is-plain-obj/compare/v3.0.0...v4.0.0) ##### Breaking - Require Node.js 12 [`69581e4`](https://togithub.com/sindresorhus/is-plain-obj/commit/69581e4) - This package is now pure ESM. Please [read this](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c).

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