Sqlite3 gem not supported on Heroku

When I tried to deploy second part of RoR tutorial to Heroku I get this error:

       An error occurred while installing sqlite3 (1.3.5), and Bundler cannot continue.
       Make sure that `gem install sqlite3 -v '1.3.5'` succeeds before bundling.
 !
 !     Failed to install gems via Bundler.
 !
 !     Detected sqlite3 gem which is not supported on Heroku.
 !     http://devcenter.heroku.com/articles/how-do-i-use-sqlite3-for-development
 !
 !     Heroku push rejected, failed to compile Ruby/rails app

To git@heroku.com:thawing-beyond-7283.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:thawing-beyond-7283.git'

I searched a little bit about this error and find this stackoverflow post. But when I look more carefully on the Gemfile syntax I found a mistake. I used simply:

gem 'sqlite3', '1.3.5'

But I should have:

group :development do
  gem 'sqlite3', '1.3.5'
end
group :production do
  gem 'pg', '0.12.2'
end

As RoR tutorial states.