chore(package): update cross-env to version 6.0.3

Closes #62

Author: greenkeeper[bot]

package.json

@@ -40,7 +40,7 @@
     "babel-jest": "^23.0.1",
     "babel-preset-env": "^1.7.0",
     "coveralls": "^3.0.1",
-    "cross-env": "^5.2.0",
+    "cross-env": "^6.0.3",
     "eslint": "^5.0.0",
     "eslint-config-airbnb-base": "^13.0.0",
     "eslint-plugin-import": "^2.13.0",