fix(deps): update dependency whatwg-fetch to v2.0.4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
whatwg-fetch	2.0.3 -> 2.0.4

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Release Notes

github/fetch (whatwg-fetch)

### [`v2.0.4`](https://togithub.com/github/fetch/blob/HEAD/CHANGELOG.md#v204) [Compare Source](https://togithub.com/github/fetch/compare/v2.0.3...v2.0.4) > 29 March 2018 - Create CONTRIBUTING.md [`#604`](https://togithub.com/JakeChampion/fetch/pull/604) - Tweak the wording of the “Read this first” section [`#553`](https://togithub.com/JakeChampion/fetch/pull/553) - Allow undefined Response status [`#534`](https://togithub.com/JakeChampion/fetch/pull/534) - Ensure cookies aren't sent if `credentials: omit` [`#526`](https://togithub.com/JakeChampion/fetch/pull/526) - Added yarn command as option to installation [`#492`](https://togithub.com/JakeChampion/fetch/pull/492) - Add global replace for processing raw headers [`#496`](https://togithub.com/JakeChampion/fetch/pull/496) - Added safari to native fetch browser support. [`#469`](https://togithub.com/JakeChampion/fetch/pull/469) - Support obs-fold as header delimiter [`#491`](https://togithub.com/JakeChampion/fetch/pull/491) - Tweak the wording of "Read this first" [`54dc3f8`](https://togithub.com/JakeChampion/fetch/commit/54dc3f823fe3e6452da8d19bf7aad7eda4cd1dd8) - Add test for undefined Response status [`0ecdd40`](https://togithub.com/JakeChampion/fetch/commit/0ecdd40c50d4bcdfd4d2a09448a6d01089dc182a) - Fix cookie test with newer versions of Node [`7831671`](https://togithub.com/JakeChampion/fetch/commit/7831671b172435c52064f588cf7145236fecf5f2)

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