title: How to get Heroku to recognize a yarn.lock or package.json within a subdirectory (not root)
body: <p>I have a Rails application using React, Webpack, and Yarn for the client side. I have everything relating to the client side within the /client directory. This includes my yarn.lock and package.json files. I have a Procfile that cds into /client and properly runs <code>yarn run build</code>. This works locally with no errors. However, when I deploy/push to Heroku, my push is rejected and I get the following error:</p>
  
  <pre><code>remote:        cd client &amp;&amp; yarn run build:production
  remote:        sh: 1: yarn: not found
  remote:        rake aborted!
  remote:        Command failed with status (127): [cd client &amp;&amp; yarn run build:production...]
  </code></pre>
  
  <p>What this says to me is that Heroku wasn't able to find a yarn.lock file in the root level. How do I get Heroku to use the <code>yarn.lock</code> file within my /client directory?</p>
  
  <p>Or is the cause of this error something else entirely?</p>