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

Closes #115

Author: greenkeeper[bot]

package.json

@@ -46,7 +46,7 @@
     "@types/node": "^8.0.34",
     "@types/shelljs": "^0.7.4",
     "ava": "^0.23.0",
-    "cross-env": "^5.0.5",
+    "cross-env": "^6.0.2",
     "cross-var": "^1.1.0",
     "husky": "^0.14.3",
     "npm-run-all": "^4.1.1",