Rails root page not displayed on heroku app

I have created an app in RoR, but the problem is that i am not able to get the root page that is "posts#index" on heroku but i am able to view it on rails local server. The route file is

Rails.application.routes.draw do
  resources :posts
  root "posts#index"
  get "/posts/new" => "posts#show"
end

I am using sqlite3 for development and test & postgreSQL for production.
And the heroku log contains error like

1. Warning: the running version of Bundler is older than the version that created the lockfile. We suggest you upgrade to the latest version of Bundler by running gem install bundler
2. Include 'rails_12factor' gem to enable all platform features.
3. No Procfile detected, using the default web server. We recommend explicitly declaring how to boot your server process via a Procfile.

A thanks in advance.