chore(deps): update dependency react to v16.8.4

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change	References
react	dependencies	patch	16.8.3 -> 16.8.4	homepage, source

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Release Notes

facebook/react

### [`v16.8.4`](https://togithub.com/facebook/react/blob/master/CHANGELOG.md#​1684-March-5-2019) [Compare Source](https://togithub.com/facebook/react/compare/v16.8.3...v16.8.4) ##### React DOM and other renderers - Fix a bug where DevTools caused a runtime error when inspecting a component that used a `useContext` hook. ([@​bvaughn](https://togithub.com/bvaughn) in [#​14940](https://togithub.com/facebook/react/pull/14940))

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