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

Closes #159

Author: greenkeeper[bot]

package.json

@@ -63,7 +63,7 @@
     "babel-plugin-istanbul": "^5.1.4",
     "chai": "^4.1.2",
     "chai-as-promised": "^7.1.1",
-    "cross-env": "^5.0.5",
+    "cross-env": "^6.0.3",
     "deep-freeze": "^0.0.1",
     "enzyme": "^3.8.0",
     "enzyme-adapter-react-16": "^1.7.1",