title: Configure Homebrew to not delete old versions
body: <p>When I install a package through homebrew, it removes the old versions.</p>
  
  <pre><code>$ brew upgrade terraform
    /usr/local/Cellar/terraform/0.11.14: 6 files, 42.4MB
  Removing: /usr/local/Cellar/terraform/0.11.13... (6 files, 120.6MB)
  Removing: /Users/vikas/Library/Caches/Homebrew/terraform--0.11.13.mojave.bottle.tar.gz... (25.4MB)
  </code></pre>
  
  <p>How can I disable this so that I can switch back to older versions.</p>
  
  <pre><code>$ brew switch [formula] [version]
  </code></pre>