simple Heroku + Rails 4 app crashing - ruby-on-rails

Question

I am at the end of Chapter 2 of Hartl's Rails Tutorial the app works locally but I can't get it to deploy.
http://quiet-ocean-3277.herokuapp.com/
$ git push heroku master
Counting objects: 3, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (2/2), 253 bytes, done.
Total 2 (delta 1), reused 0 (delta 0)
-----> Ruby/Rails app detected
-----> Using Ruby version: ruby-1.9.3
-----> Installing dependencies using Bundler version 1.3.2
Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin --deployment
Using rake (10.1.0)
Using i18n (0.6.4)
Using minitest (4.7.5)
Using multi_json (1.7.7)
Using atomic (1.1.10)
Using thread_safe (0.1.0)
Using tzinfo (0.3.37)
Using activesupport (4.0.0)
Using builder (3.1.4)
Using erubis (2.7.0)
Using rack (1.5.2)
Using rack-test (0.6.2)
Using actionpack (4.0.0)
Using mime-types (1.23)
Using polyglot (0.3.3)
Using treetop (1.4.14)
Using mail (2.5.4)
Using actionmailer (4.0.0)
Using activemodel (4.0.0)
Using activerecord-deprecated_finders (1.0.3)
Using arel (4.0.0)
Using activerecord (4.0.0)
Using coffee-script-source (1.6.3)
Using execjs (1.4.0)
Using coffee-script (2.2.0)
Using thor (0.18.1)
Using railties (4.0.0)
Using coffee-rails (4.0.0)
Using hike (1.2.3)
Using jbuilder (1.0.2)
Using jquery-rails (2.2.1)
Using json (1.8.0)
Using pg (0.15.1)
Using bundler (1.3.2)
Using tilt (1.4.1)
Using sprockets (2.10.0)
Using sprockets-rails (2.0.0)
Using rails (4.0.0)
Using rails_serve_static_assets (0.0.1)
Using rails_stdout_logging (0.0.1)
Using rails_12factor (0.0.2)
Using rdoc (3.12.2)
Using sass (3.2.9)
Using sass-rails (4.0.0)
Using sdoc (0.3.20)
Using turbolinks (1.1.1)
Using uglifier (2.1.1)
Your bundle is complete! It was installed into ./vendor/bundle
Cleaning up the bundler cache.
-----> Writing config/database.yml to read from DATABASE_URL
-----> Preparing app for Rails asset pipeline
Running: rake assets:precompile
Asset precompilation completed (7.52s)
Cleaning assets
-----> WARNINGS:
You have not declared a Ruby version in your Gemfile.
To set your Ruby version add this line to your Gemfile:
ruby '1.9.3'
# See https://devcenter.heroku.com/articles/ruby-versions for more information."
-----> Discovering process types
Procfile declares types -> (none)
Default types for Ruby/Rails -> console, rake, web, worker
-----> Compiled slug size: 20.0MB
-----> Launching... done, v8
http://quiet-ocean-3277.herokuapp.com deployed to Heroku
To git#heroku.com:quiet-ocean-3277.git
2d25f33..322b9e4 master -> master
All looks good except the app crashes. In the logs:
2013-07-17T23:56:21.430674+00:00 heroku[web.1]: State changed from starting to crashed
2013-07-18T00:00:36.148404+00:00 heroku[web.1]: State changed from crashed to starting
2013-07-18T00:00:39.933663+00:00 heroku[web.1]: Starting process with command `bin/rails server -p 40617 -e $RAILS_ENV`
2013-07-18T00:00:41.477904+00:00 app[web.1]: /usr/bin/env: ruby1.9.1: No such file or directory
2013-07-18T00:00:42.674144+00:00 heroku[web.1]: Process exited with status 127
Why is it calling Ruby 1.9.1 and crashing ? Here's the gemfile:
source 'https://rubygems.org'
#ruby '1.9.3'
#ruby-gemset=railstutorial_rails_4_0
gem 'rails', '4.0.0'
group :development do
gem 'sqlite3', '1.3.7'
end
gem 'sass-rails', '4.0.0'
gem 'uglifier', '2.1.1'
gem 'coffee-rails', '4.0.0'
gem 'jquery-rails', '2.2.1'
gem 'turbolinks', '1.1.1'
gem 'jbuilder', '1.0.2'
group :doc do
gem 'sdoc', '0.3.20', require: false
end
group :production do
gem 'pg', '0.15.1'
gem 'rails_12factor', '0.0.2'
end

Answer 1

I had same problem. I solved it by repacement "#!/usr/bin/env ruby1.9.1" => "#!/usr/bin/env ruby" in 3 files:
bin/bundle
bin/rails
bin/rake

Answer 2

Short answer, you need to specify the ruby version in the Gemfile. It looks like you have it commented out. Heroku uses ruby v1.9.1 by default
This answer links to a gist with steps you can follow to make sure your local and heroku set up are correct.

Answer 3

I would recommend placing:
ruby '2.0.0'
in your Gemfile towards the top. Ruby 2.0.0 contains many changes that increase performance and it works better with Rails 4.