chore(package): update async to version 2.0.0

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -41,7 +41,7 @@
     "test": "grunt"
   },
   "dependencies": {
-    "async": "~1.5.2",
+    "async": "~2.0.0",
     "deep-extend": "^0.4.1",
     "jwt-simple": "~0.4.0",
     "memcached": "~2.2.2",