title: Error: Unable to 'pub upgrade' flutter tool. Retrying in five seconds
body: <p>Log:</p>
  <blockquote>
  <p>E:\Flutter&gt;flutter doctor Checking Dart SDK version... Downloading
  Dart SDK from Flutter engine ead227f a... Unzipping Dart SDK...
  Updating flutter tool... Error: Unable to 'pub upgrade' flutter tool.
  Retrying in five seconds...</p>
  <p>Waiting for 0 seconds, press CTRL+C to quit ... Error: Unable to 'pub
  upgrade' flutter tool. Retrying in five seconds...</p>
  <p>Waiting for 0 seconds, press CTRL+C to quit ... Error: Unable to 'pub
  upgrade' flutter tool. Retrying in five seconds...</p>
  <p>Waiting for 0 seconds, press CTRL+C to quit ... Error: Unable to 'pub
  upgrade' flutter tool. Retrying in five seconds...</p>
  <p>Waiting for 0 seconds, press CTRL+C to quit ... Error: Unable to 'pub
  upgrade' flutter tool. Retrying in five seconds...</p>
  <p>Waiting for 0 seconds, press CTRL+C to quit ... Error: Unable to 'pub
  upgrade' flutter tool. Retrying in five seconds...</p>
  </blockquote>
  <p><a href="https://i.stack.imgur.com/rf4RV.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rf4RV.jpg" alt="enter image description here" /></a></p>