title: Gem::LoadError: Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile
body: <p>I'm new to Rails. This application works fine on my local machine, and deploys without any problem. But when I run <code>heroku run rake db:migrate</code>, I get this error:</p>
  
  <pre><code>Running `rake db:migrate` attached to terminal... up, run.1269
  rake aborted!
  Gem::LoadError: Specified 'postgresql' for database adapter, but the gem is not loaded. Add `gem 'pg'` to your Gemfile.
  </code></pre>