App crashed H10 error code, when uploading to Heroku

I have a node app, which is running locally without any problem, but when I try to deploy it with heroku, I cannot do it. The error that I get is:

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

I am using the mongoLab at my application, but I added it as addon in heroku. Here is the server.js:

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"
  }
}

Please, let me know if you have any suggestion, as I am trying to solve this for hours.

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