Rails App not Precompiling for Heroku Push

Question

I am new to both Ruby and Ruby on Rails. To begin familiarizing myself with the framework, I am going through One Month Rails. Unfortunately, I have hit a snag. Up until last night, I was able to push my app changes to Heroku. Now, however, whenever I try to push changes through, I get this error.

-----> Writing config/database.yml to read from DATABASE_URL -----> Preparing app for Rails asset pipeline Running: rake assets:precompile rake aborted! couldn't find file 'bootstrap'

This is after bundle install(ing) -> git add . -> git commit -> git push. I have done quite a bit of googling, but just can't seem to figure it out. Any help is much appreciated! Thanks!

I am attaching my Gemfile.

Source 'https://rubygems.org'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.0.0'
gem 'jquery-rails'
gem 'devise'
gem 'simple_form'
gem 'protected_attributes'

# Use sqlite3 as the database for Active Record
group :production do
    gem 'pg'
    gem 'rails_12factor'
end

group :development, :test do
    gem 'sqlite3'
    gem 'sass-rails', '~> 4.0.0'
    gem 'bootstrap-sass', '~> 2.3.2.1'
    gem 'uglifier', '>= 1.3.0'
    gem 'coffee-rails', '~> 4.0.0'
    gem 'turbolinks'
    gem 'jbuilder', '~> 1.2'
end

group :doc do
  gem 'sdoc', require: false
end

Answer 1

Move out following gems from group :development, :test

gem 'sass-rails', '~> 4.0.0'
gem 'bootstrap-sass', '~> 2.3.2.1'
gem 'uglifier', '>= 1.3.0'
gem 'coffee-rails', '~> 4.0.0'
gem 'turbolinks'
gem 'jbuilder', '~> 1.2'

Heroku tries to compile files for production, not for development and testing.