chore(deps): update dependency nexmo to v2

Author: mend-for-github-com[bot]

package.json

@@ -21,7 +21,7 @@
     "body-parser": "^1.15.2",
     "dotenv": "^2.0.0",
     "express": "^4.14.0",
-    "nexmo": "^1.0.0-beta-7"
+    "nexmo": "^2.2.1"
   },
   "devDependencies": {
     "nodemon": "^1.10.0"