add co dependency

Author: Frand

package.json

@@ -31,7 +31,8 @@
     "moment": "^2.12.0",
     "mongoose": "4.4.7",
     "underscore": "^1.8.3",
-    "validator": "^5.1.0"
+    "validator": "^5.1.0",
+    "co": "4.6.0"
   },
   "devDependencies": {
     "chai": "^3.5.0",