chore(package): update mqtt to version 2.13.0

Closes #10

Author: greenkeeper[bot]

package.json

@@ -22,7 +22,7 @@
     "chai": "~4.1.0",
     "coffee-script": "^1.8.0",
     "mocha": "~3.3.0",
-    "mqtt": "~1.4.0",
+    "mqtt": "~2.13.0",
     "msgflo": "^0.10.0"
   },
   "keywords": [],