title: Push Respond CMS to Heroku: no 'composer.lock' was found
body: <p>I want to host Respond CMS on Heroku, so I did:</p>
  
  <ol>
  <li><code>git clone</code> of the respondcms repository</li>
  <li><code>heroku</code> create in that folder</li>
  <li><code>git push heroku master</code></li>
  </ol>
  
  <p>I always get the following error in the terminal:</p>
  
  <pre><code>remote: -----&gt;PHP app detected
  remote:
  remote:  !     ERROR: Your 'composer.json' lists dependencies inside 'require',
  remote:        but no 'composer.lock' was found. Please run 'composer update' to
  remote:        re-generate 'composer.lock' if necessary, and commit it into your
  remote:        repository. For more information, please refer to the docs at
  remote:        https://devcenter.heroku.com/articles/php-support#activation
  remote:
  remote:
  remote:  !     Push rejected, failed to compile PHP app
  remote:
  remote: Verifying deploy...
  remote:
  remote: !       Push rejected to app-name
  </code></pre>
  
  <p>I ran <code>composer update</code> and that works fine, also there is a <code>composer.lock</code> file in the folder.</p>
  
  <p>Why isn't this working?</p>