fix(package): update fs-extra to version 4.0.1

Closes #28

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
   "license": "MIT",
   "dependencies": {
     "commondir": "^1.0.1",
-    "fs-extra": "^1.0.0",
+    "fs-extra": "^4.0.1",
     "yargs": "^6.0.0",
     "glob": "^7.0.3",
     "rev-hash": "^1.0.0",