New Rails app Postgres won't install

Question

I just started a Rails 4 app from scratch with the intention to use Postgres. I went and changed the database.yml file to the following:

development:
  adapter: postgresql
  encoding: unicode
  database: personalapi_dev
  pool: 5
  username: nickoneill
  password:
  host: localhost  

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test: &test
  adapter: postgresql
  encoding: unicode
  database: personalapi_test
  pool: 5
  username: nickoneill
  password:
  host: localhost  

Yet when I run rake db:create it gives me the following error:

uninitialized constant ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::PG
/Users/nickoneill/.rvm/gems/ruby-2.0.0-p247@personalapi/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql_adapter.rb:562:in `active?'
/Users/nickoneill/.rvm/gems/ruby-2.0.0-p247@personalapi/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:360:in `verify!'
/Users/nickoneill/.rvm/gems/ruby-2.0.0-p247@personalapi/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:458:in `block in checkout_and_verify'
/Users/nickoneill/.rvm/gems/ruby-2.0.0-p247@personalapi/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:373:in `_run__1536634998624253346__checkout__callbacks'
/Users/nickoneill/.rvm/gems/ruby-2.0.0-p247@personalapi/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:80:in `run_callbacks'

I've tried everything from upgrading the Postgres gem, making sure Postgres is running, etc, yet not sure why it's not working. I have other rails apps (including Rails 4) on my computer that run just fine yet this new one won't work. Any ideas?

Update

Here's my gemfile:

source 'https://rubygems.org'
ruby "2.0.0"

# gem 'bootstrap-sass', '~> 2.3.2'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.0.0'
gem 'addressable'

#
# Error handling
#
gem "sentry-raven" #, :git => "https://github.com/getsentry/raven-ruby.git"

#
# Sidekiq gems
#
gem 'sidekiq' , '2.5.4'
gem 'redis' , '~> 3.0'
gem 'unicorn' , '~> 4.5'

# For sidekiq interface
#gem 'sinatra', require: false
gem 'slim'
gem 'sinatra', '>= 1.3.0', :require => nil

# json parsing
gem 'oj' , '2.0.1'

# templates
gem 'haml'

# file storage
# gem "paperclip", "~> 3.1"
# gem 'aws-sdk', '1.8.0'

# Use postgres as the database for Active Record
gem 'pg'

# Use SCSS for stylesheets
gem 'sass-rails', '~> 4.0.0'

# 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', '~> 1.2'

group :doc do
  # bundle exec rake doc:rails generates the API under doc/api.
  gem 'sdoc', require: false
end

group :development , :test do
    gem "better_errors"
    gem 'fakeweb'
    gem 'rspec-rails', '2.12.2'
    gem 'shoulda-matchers'
    gem 'guard-rspec'
end

group :test do 
    #gem "cucumber-rails", ">= 1.3.0"
    gem 'database_cleaner'
    gem 'factory_girl_rails' , '~> 4.0'
    gem 'capybara'
    gem 'guard-spork'
    gem 'spork'
    gem "launchy"
    gem 'rb-fsevent', '~> 0.9.1'
    gem 'faker'
    gem 'annotate'
    gem 'simplecov'
    gem 'guard-rspec'
    gem 'growl'
    gem 'rb-fsevent', '~> 0.9.1'
end

Answer 1

根据我将Gemfile更新为gem'pg'的经验，'0.15.1'解决了这个问题。