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

Closes #24

Author: greenkeeper[bot]

package.json

@@ -27,7 +27,7 @@
     "babel-preset-env": "^1.6.0",
     "chai": "^4.1.2",
     "chance": "^1.0.12",
-    "cross-env": "^5.1.1",
+    "cross-env": "^6.0.2",
     "eslint": "^4.13.1",
     "eslint-config-standard": "^11.0.0",
     "eslint-plugin-import": "^2.8.0",