fix(package): update pkg-dir to version 3.0.0 (#384)

Author: greenkeeper[bot]

package.json

@@ -72,7 +72,7 @@
     "lodash": "^4.15.0",
     "mkdirp": "^0.5.1",
     "node-object-hash": "^1.2.0",
-    "pkg-dir": "^2.0.0",
+    "pkg-dir": "^3.0.0",
     "rimraf": "^2.6.2",
     "tapable": "^1.0.0-beta.5",
     "webpack-sources": "^1.0.1",