chore(package): update fs-extra to version 8.1.0

Closes #53

Author: greenkeeper[bot]

package.json

@@ -46,7 +46,7 @@
     "chai-as-promised": "^7.1.1",
     "coveralls": "^3.0.0",
     "cross-env": "^5.1.3",
-    "fs-extra": "^5.0.0",
+    "fs-extra": "^8.1.0",
     "globule": "^1.2.0",
     "hard-rejection": "^1.0.0",
     "in-publish": "^2.0.0",