build(deps-dev): update cross-env requirement from ^5.2.0 to ^6.0.0

Updates the requirements on [cross-env](https://github.com/kentcdodds/cross-env) to permit the latest version.
- [Release notes](https://github.com/kentcdodds/cross-env/releases)
- [Changelog](https://github.com/kentcdodds/cross-env/blob/master/CHANGELOG.md)
- [Commits](https://github.com/kentcdodds/cross-env/compare/v5.2.0...v6.0.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -91,7 +91,7 @@
     "@umijs/fabric": "^1.1.0",
     "chalk": "^2.4.2",
     "check-prettier": "^1.0.3",
-    "cross-env": "^5.2.0",
+    "cross-env": "^6.0.0",
     "cross-port-killer": "^1.1.1",
     "enzyme": "^3.9.0",
     "eslint": "^5.16.0",