Update petstore sample for changes on PR #3212

Author: pjmolina

samples/server/petstore/nodejs/README.md

@@ -8,11 +8,10 @@ This example uses the [expressjs](http://expressjs.com/) framework.  To see how
 [README](https://github.com/swagger-api/swagger-codegen/blob/master/README.md)
 
 ### Running the server
-To run the server, follow these simple steps:
+To run the server, run:
 
 ```
-npm install
-node .
+npm start
 ```
 
 To view the Swagger UI interface:

samples/server/petstore/nodejs/package.json

@@ -3,6 +3,10 @@
   "version": "1.0.0",
   "description": "This is a sample server Petstore server.  You can find out more about Swagger at [http://swagger.io](http://swagger.io) or on [irc.freenode.net, #swagger](http://swagger.io/irc/).  For this sample, you can use the api key `special-key` to test the authorization filters.",
   "main": "index.js",
+  "scripts": {
+    "prestart": "npm install",
+    "start": "node index.js"
+  },    
   "keywords": [
     "swagger"
   ],