我有一个node app，它正在本地运行，没有任何问题，但当我尝试用heroku部署它时，我做不到。我得到的错误是：

2017-05-26T13:37:31.249587+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=engageitvisz.herokuapp.com request_id=e9641b76-0667-44ce-b85a-fb431c1cca2a fwd="31.10.149.171" dyno= connect= service= status=503 bytes= protocol=https

null

var express = require('express');
var app = express();

var databaseUrl = "mongodb://user:pass@ds137090.mlab.com:37090/questions"; 
var collections = ["questions"];
var mongojs = require('mongojs');
var db = mongojs(databaseUrl, collections);

app.set('port', (process.env.PORT || 5002));

var bodyParser = require('body-parser');
app.use(express.static(__dirname + "/public"));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}));
app.get('/', function(request, response){
   response.send("Hello from server.js");
});

app.get('/questions', function(request, response){
   console.log("I received a GET request for questions");

db.questions.find(function(err, docs){
  if(err){
         response.send(err);
  }
  response.json(docs);
   })
});
app.post('/questions', function(request, response){
   console.log("I received a POST request for questions");

});

app.listen(app.get('port'), function(){
   console.log('Server running on port', app.get('port'));
});

procfile：

web: node server.js

package.json：

{
  "name": "engageit",
  "version": "1.0.0",
  "description": "EngageIt visualization",
  "main": "server.js",
  "dependencies": {
    "express": "4.13.1"
  },
  "repository": {
     "type": "git",
     "url": "https://github.com/VitezKoja92/EngageItVisz.git"
  },
  "scripts": {
    "test": "test",
    "start": "node server.js",
    "heroku-prebuild": "echo This runs before Heroku installs your dependencies.",
    "heroku-postbuild": "echo This runs afterwards."
  },
  "author": "Danilo Krasic",
  "license": "ISC",
  "keywords": [
    "node",
    "heroku",
    "express"
  ],
  "engines": {
    "node": "7.7.2"
  }
}

请让我知道，如果你有任何建议，因为我正在努力解决这几个小时。