title: Why is devDependencies' pruning skipped even if NPM_CONFIG_PRODUCTION is true?
body: <p>When trying to push a Node.js project to Heroku, I can find between the log lines the following one:</p>
  
  <pre><code>Pruning devDependencies
  remote:        Skipping because NPM_CONFIG_PRODUCTION is 'true'
  </code></pre>
  
  <p>Now, I was expecting pruning is skipped at the opposite condition (<code>NPM_CONFIG_PRODUCTION=false</code>).</p>
  
  <p>Any thoughts about?</p>