title: Gem::LoadError: Error loading the 'sqlite3' Active Record adapter
body: <p>I am doing <code>heroku run rake db:migrate</code>
  and this is the error:</p>
  
  <blockquote>
    <p>Gem::LoadError: Error loading the 'sqlite3' Active Record adapter.
    Missing a gem it depends on? sqlite3 is not part of the bundle. Add it
    to your Gemfile.</p>
  </blockquote>
  
  <p><strong>Gemfile:</strong></p>
  
  <pre><code>group :production do
    gem 'pg', '~&gt; 0.18'
  end
  
  group :development, :test do
    # Call 'byebug' anywhere in the code to stop execution and get a debugger console
    gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
    # Use sqlite3 as the database for Active Record
    gem 'sqlite3'
  end
  
  group :development do
    # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
    gem 'web-console', '&gt;= 3.3.0'
    gem 'listen', '&gt;= 3.0.5', '&lt; 3.2'
    # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
    gem 'spring'
    gem 'spring-watcher-listen', '~&gt; 2.0.0'
  end
  
  group :test do
    # Adds support for Capybara system testing and selenium driver
    gem 'capybara', '&gt;= 2.15'
    gem 'selenium-webdriver'
    # Easy installation and use of chromedriver to run system tests with Chrome
    gem 'chromedriver-helper'
  end
  </code></pre>
  
  <p><strong>Database.yml</strong></p>
  
  <pre><code>production:
    adapter: postgresql
    encoding: Unicode    
  </code></pre>