title: replace yarn version v1.0.0 to v0.28.4
body: <p>I currently used nightly builds to update my yarn and I'm using yarn v1.0.0-20170906.0822. </p>
  
  <p>But it had a serious problem which is blocking deployment on Heroku.</p>
  
  <p>So, I searched a way to migrate from v1.0.0xx to v0.28.4.</p>
  
  <p>I tried to remove it using <code>brew uninstall yarn</code> however it failed to delete yarn so I can still v1.0.0xx shown when I hit <code>yarn --version</code> on the terminal.</p>
  
  <p>I remember I installed yarn via brew, not npm.</p>
  
  <p>Are there any other options to delete yarn and replace it with v0.28.4?</p>