adding mongoose promise

ChatService/server.js

@@ -9,7 +9,8 @@ var methodOverride = require('method-override');
 var port = process.env.PORT || 3000; // set our port
 mongoose.connect("mongodb://127.0.0.1:27017/chatservice", {
     useMongoClient: true
-}); // connect to our mongoDB database
+});
+mongoose.Promise = global.Promise; // connect to our mongoDB database
 
 // get all data/stuff of the body (POST) parameters
 app.use(bodyParser.json()); // parse application/json