Bump cross-env from 5.2.1 to 6.0.0

Bumps [cross-env](https://github.com/kentcdodds/cross-env) from 5.2.1 to 6.0.0.
- [Release notes](https://github.com/kentcdodds/cross-env/releases)
- [Changelog](https://github.com/kentcdodds/cross-env/blob/master/CHANGELOG.md)
- [Commits](kentcdodds/cross-env@v5.2.1...v6.0.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

npm-shrinkwrap.json

@@ -118,7 +118,7 @@
 	"devDependencies": {
 		"ava": "^2.4.0",
 		"coveralls": "^3.0.6",
-		"cross-env": "^5.2.1",
+		"cross-env": "^6.0.0",
 		"docdash": "^1.1.1",
 		"eslint": "^5.16.0",
 		"eslint-config-google": "^0.14.0",