title: git reset --hard didn't help me with rake db:migrate
body: <p>When I tried to change my Rails database from Sqlite to Postgres, I ran into problems. Then, I decided to go back to a git commit when everything was working. With:</p>
  
  <pre><code>git reset --hard 52ca294cd88de9aaa1c00c95e2cdabd744cd7499
  </code></pre>
  
  <p>I have done <code>bundle install</code>. Now when I do <code>rake db:migrate</code> I get this message:</p>
  
  <blockquote>
    <p>rake aborted!
    Gem::LoadError: Specified 'postgresql' for database adapter, but the gem is not loaded. Add <code>gem 'pg'</code> to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).</p>
  </blockquote>
  
  <p>I don't understand, at this commit everything was working well in Sqlite3. Thanks</p>