fix(package): update commander to version 4.0.1

Closes #41

Author: greenkeeper[bot]

package.json

@@ -50,7 +50,7 @@
     "rimraf": "2.6.2"
   },
   "dependencies": {
-    "commander": "^2.9.0",
+    "commander": "^4.0.1",
     "cross-spawn": "^5.0.1",
     "debug": "^3.0.0",
     "mkdirp": "^0.5.1",