fix(package): update update-notifier to version 4.0.0

Closes #33

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
     "digitalocean": "^0.10.0",
     "lodash": "^4.15.0",
     "public-ip": "^2.1.0",
-    "update-notifier": "^2.1.0"
+    "update-notifier": "^4.0.0"
   },
   "devDependencies": {
     "mocha": "^5.0.0",