title: heroku rake db:migrate fails
body: <p>I get the following error:</p>
  <blockquote>
  <p>[app (master)]$ <strong>heroku rake db:migrate</strong></p>
  <p>rake aborted!</p>
  <p>undefined method `root' for Heroku::Rails:Module /app/Rakefile:7</p>
  <p>(See full trace by running task with --trace) (in /app)</p>
  </blockquote>
  <p>I can't figure out how to run trace as suggested by the error (<code>heroku rake db:migrate --trace</code>
  gives &quot;Invalid Option --trace&quot;), and I don't believe this is related to the well-known &quot;heroku doesn't use sqlite3&quot; issue.</p>
  <p>My Rakefile is as follows:</p>
  <pre><code>require File.expand_path('../config/application', __FILE__)
  require 'rake'
  
  SampleApp::Application.load_tasks
  </code></pre>