Travis CI can't find 'pg' gem - ruby-on-rails

Question

I'm using Travis CI to test my Rails project.
When it build my commit, it stops on bundle exec rake.
Part of log:
$ gem --version
2.2.2
$ bundle --version
Bundler version 1.6.2
$ bundle install --jobs=3 --retry=3 --deployment
Fetching gem metadata from https://rubygems.org/..........
Fetching additional metadata from https://rubygems.org/..
Installing i18n 0.6.11
Installing rake 10.3.2
Installing minitest 5.4.0
Installing thread_safe 0.3.4
Installing builder 3.2.2
Installing json 1.8.1
Installing erubis 2.7.0
Installing mime-types 1.25.1
Installing rack 1.5.2
Installing polyglot 0.3.5
Installing arel 5.0.1.20140414130214
Installing execjs 2.2.1
Installing coffee-script-source 1.7.1
Installing thor 0.19.1
Installing hike 1.2.3
Using bundler 1.6.2
Installing multi_json 1.10.1
Installing tilt 1.4.1
Installing rails_serve_static_assets 0.0.2
Installing rails_stdout_logging 0.0.3
Installing tzinfo 1.2.1
Installing sass 3.2.19
Installing rack-test 0.6.2
Installing rdoc 4.1.1
Installing treetop 1.4.15
Installing coffee-script 2.3.0
Installing uglifier 2.5.3
Installing sprockets 2.11.0
Installing rails_12factor 0.0.2
Installing sdoc 0.4.0
Installing activesupport 4.1.4
Installing mail 2.5.4
Installing actionview 4.1.4
Installing jbuilder 2.1.3
Installing activemodel 4.1.4
Installing actionpack 4.1.4
Installing activerecord 4.1.4
Installing railties 4.1.4
Installing sprockets-rails 2.1.3
Installing actionmailer 4.1.4
Installing coffee-rails 4.0.1
Installing jquery-rails 3.1.1
Installing sass-rails 4.0.3
Installing turbolinks 2.2.2
Installing rails 4.1.4
Your bundle is complete!
It was installed into ./vendor/bundle
Post-install message from rdoc:
Depending on your version of ruby, you may need to install ruby rdoc/ri data:
<= 1.8.6 : unsupported
= 1.8.7 : gem install rdoc-data; rdoc-data --install
= 1.9.1 : gem install rdoc-data; rdoc-data --install
>= 1.9.2 : nothing to do! Yay!
$ psql -c 'create database travis_ci_test;' -U postgres
CREATE DATABASE
$ cp config/database.yml.travis config/database.yml
$ bundle exec rake
rake aborted!
Gem::LoadError: Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
(As you can see, there is no pg gem installed).
My .travis.yml:
language: ruby
rvm:
- "2.0.0"
addons:
postgresql: "9.3"
before_script:
- psql -c 'create database travis_ci_test;' -U postgres
- cp config/database.yml.travis config/database.yml
My Gemfile:
source 'https://rubygems.org'
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.1.4'
# Use postgresql as the database for Active Record
gem 'pg'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 4.0.3'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .js.coffee assets and views
gem 'coffee-rails', '~> 4.0.0'
# See https://github.com/sstephenson/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby
# Use jquery as the JavaScript library
gem 'jquery-rails'
# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.0'
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', '~> 0.4.0', group: :doc
# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw]
gem 'rails_12factor', group: :production
ruby "2.0.0"
So 'pg' gem is in the Gemfile and it works on my computer, but Travis doesn't install it.

Answer 1

Is the 'pg' gem in your Gemfile.lock file? If not, you may need to delete this file and regenerate it by running bundle install again.

Answer 2

Removing Gemfile.lock from the repository worked, now build and testing is working as expected.
I guess that happens because of lock-file being created on Windows, and it includes some platform-specific stuff (like mingw32 suffixes for gems)