Bump cross-env from 5.2.1 to 6.0.3

Bumps [cross-env](https://github.com/kentcdodds/cross-env) from 5.2.1 to 6.0.3.
- [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...v6.0.3)

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

Author: dependabot-preview[bot]

package.json

@@ -68,7 +68,7 @@
     "chromedriver": "75.1.0",
     "clean-css-cli": "^4.1.6",
     "commander": "^2.15.1",
-    "cross-env": "^5.2.0",
+    "cross-env": "^6.0.3",
     "css-loader": "^0.28.11",
     "es3ify-loader": "^0.2.0",
     "eslint": "^4.6.1",