fix(package): update async to version 3.1.0

Closes #228

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
   ],
   "dependencies": {
     "amqplib": "^0.5.1",
-    "async": "^2.5.0",
+    "async": "^3.1.0",
     "coffeescript": "^2.0.2",
     "commander": "^2.10.0",
     "debug": "^4.0.0",