chore(deps): update dependency defu to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
defu	^3.2.2 -> ^4.0.1

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Release Notes

unjs/defu

### [`v4.0.1`](https://togithub.com/unjs/defu/blob/master/CHANGELOG.md#​401-httpsgithubcomunjsdefucomparev400v401-2021-04-23) [Compare Source](https://togithub.com/unjs/defu/compare/v4.0.0...v4.0.1) ### [`v4.0.0`](https://togithub.com/unjs/defu/blob/master/CHANGELOG.md#​400-httpsgithubcomunjsdefucomparev322v400-2021-04-23) [Compare Source](https://togithub.com/unjs/defu/compare/v3.2.2...v4.0.0) ##### :warning: BREAKING CHANGES - module exports ##### Features - module exports ([42df406](https://togithub.com/unjs/defu/commit/42df406b6938bc7ffb5f628efaa9447c4e95b211)) ##### [3.2.2](https://togithub.com/unjs/defu/compare/v3.2.1...v3.2.2) (2020-11-10) ##### Bug Fixes - switch back to bili for es5 support till fixing in siroc ([07786c2](https://togithub.com/unjs/defu/commit/07786c270f9bf49529d8203f31b4b9bd696a6ee3)) ##### [3.2.1](https://togithub.com/unjs/defu/compare/v3.2.0...v3.2.1) (2020-11-09) ##### Bug Fixes - **types:** correct type inference where merged types are same ([#​26](https://togithub.com/unjs/defu/issues/26)) ([f322607](https://togithub.com/unjs/defu/commit/f322607515a5bd19b1a2f28d7e3336fee9194520))

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