title: `fastboot devices` not listing coral dev board
body: <p>I'm trying to flash the coral dev board following the steps at <a href="https://coral.withgoogle.com/docs/dev-board/get-started/#flash-the-board" rel="nofollow noreferrer">https://coral.withgoogle.com/docs/dev-board/get-started/#flash-the-board</a>.</p>
  
  <p>I have the serial connection working and can run <code>fastboot 0</code> in <code>u-boot</code> on the board. However, when I run <code>fastboot devices</code> on my machine, nothing appears.</p>
  
  <p>I'm on MacOS 10.14.6 with fastboot version 29.0.2-5738569 and have installed the CP210x USB drivers for MacOS.</p>