fix(package): update commander to version 4.0.0

Closes #33

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
   "dependencies": {
     "async": "^2.1.5",
     "check-types": "^7.1.5",
-    "commander": "^2.9.0",
+    "commander": "^4.0.0",
     "escomplex": "2.0.0-alpha",
     "esprima": "^3.1.3"
   },