Update dependency cross-env to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
cross-env	devDependencies	major	^5.2.1 -> ^6.0.3

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Release Notes

kentcdodds/cross-env

v6.0.3

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Bug Fixes

• do not compile anything (67f21c3)

v6.0.2

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Bug Fixes

• table of contents in README (a825e9c)

v6.0.1

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Bug Fixes

• update all packages, tests, and README (36bb6c3)

v6.0.0

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Bug Fixes

• bumped cross-spawn to version 7.0.0 (#​211) (61ebf59)

BREAKING CHANGES

• Drop support for Node.js < 7.

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[coveralls]

Pull Request Test Coverage Report for Build 238

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.724%

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Totals
Change from base Build 234:	0.0%
Covered Lines:	725
Relevant Lines:	746

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💛 - Coveralls