title: How to unpin gdb for uninstall?
body: <p>I tried <code>$ brew uninstall gdb</code> and <code>$ brew rm gdb</code>, but it didn't work for me, because I need to unpin it at first. My error message:</p>
  
  <pre><code>Error: gdb is pinned. You must unpin it to uninstall.
  </code></pre>
  
  <p>How can I unpin the gdb?</p>