Merge pull request #6 from openstax/greenkeeper/commander-2.17.0

Update commander to the latest version 🚀

Author: philschatz

package.json

@@ -9,7 +9,7 @@
   "dependencies": {
     "bunyan": "^1.8.12",
     "bunyan-format": "^0.2.1",
-    "commander": "2.16.0",
+    "commander": "2.17.0",
     "css-tree": "1.0.0-alpha25",
     "dotenv": "^6.0.0",
     "phantomjs-prebuilt": "2.1.16",