fix(package): update walkdir to version 0.4.0

Closes #30

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
     "request": "^2.83.0",
     "revalidator": "^0.3.1",
     "walk": "^2.3.9",
-    "walkdir": "0.0.12",
+    "walkdir": "0.4.0",
     "xml2js": "^0.4.19"
   },
   "devDependencies": {