fix(package): update public-ip to version 3.1.0

Closes #29

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
     "bluebird": "^3.4.6",
     "digitalocean": "^0.10.0",
     "lodash": "^4.15.0",
-    "public-ip": "^2.1.0",
+    "public-ip": "^3.1.0",
     "update-notifier": "^2.1.0"
   },
   "devDependencies": {