fix(package): update commander to version 4.1.1

Closes #43

Author: greenkeeper[bot]

package.json

@@ -48,7 +48,7 @@
   },
   "dependencies": {
     "cli-prompt": "^0.6.0",
-    "commander": "^2.8.1",
+    "commander": "^4.1.1",
     "debug": "^2.6.8",
     "mkdirp": "^0.5.1"
   },