chore(package): update cross-env to version 6.0.1

Closes #15

Author: greenkeeper[bot]

package.json

@@ -52,7 +52,7 @@
     "babel-plugin-istanbul": "^4.1.5",
     "babel-preset-env": "^1.6.1",
     "coveralls": "^3.0.0",
-    "cross-env": "^5.1.3",
+    "cross-env": "^6.0.1",
     "mdprepare": "^1.0.0",
     "mocha": "^5.0.0",
     "nyc": "^12.0.2",