Update dependency cross-env to v7

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
cross-env	devDependencies	major	^6.0.0 -> ^7.0.0

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Release Notes

kentcdodds/cross-env

### [`v7.0.0`](https://togithub.com/kentcdodds/cross-env/releases/v7.0.0) [Compare Source](https://togithub.com/kentcdodds/cross-env/compare/v6.0.3...v7.0.0) ##### Features - update dependencies ([#​223](https://togithub.com/kentcdodds/cross-env/issues/223)) ([4ec6f40](https://togithub.com/kentcdodds/cross-env/commit/4ec6f4009d05c571d1737306cb787499d511048b)) ##### BREAKING CHANGES - Drop Node 8 support

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