chore(package): update async to version 1.5.1

http://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -68,7 +68,7 @@
     "qs": "^5.2.0"
   },
   "dependencies": {
-    "async": "~1.5.0",
+    "async": "~1.5.1",
     "cookie": "~0.2.2",
     "csv-stringify": "~0.0.8",
     "extend": "~3.0.0",