chore(package): update cross-env to version 6.0.2

Closes #47

Author: greenkeeper[bot]

package.json

@@ -46,7 +46,7 @@
     "babel-loader": "8.0.6",
     "babel-plugin-styled-components": "^1.10.0",
     "coveralls": "^3.0.2",
-    "cross-env": "^5.2.0",
+    "cross-env": "^6.0.2",
     "css-loader": "^2.0.0",
     "enzyme": "^3.7.0",
     "enzyme-adapter-react-16": "^1.6.0",