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

Closes #2

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "nyc": "^11.2.1"
   },
   "dependencies": {
-    "fs-extra": "^4.0.2",
+    "fs-extra": "^8.1.0",
     "promise": "^8.0.1",
     "watchjs": "0.0.0"
   }