fix(package): update pkg-dir to version 4.1.0

Closes #13

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
   },
   "homepage": "https://github.com/lukechilds/this",
   "dependencies": {
-    "pkg-dir": "^2.0.0"
+    "pkg-dir": "^4.1.0"
   },
   "devDependencies": {
     "ava": "^0.25.0",