title: Can't upgrade vue cli due to repeating "Please run npm install -g @vue/cli-upgrade and try again."
body: <p>I've tried to upgrade <strong>vue cli,</strong> and noticed that I need to install <strong>@vue/cli-upgrade</strong>.</p>
  
  <pre><code>ueda@klingsor:~/ml$ sudo vue upgrade
  
    Command vue upgrade requires a global addon to be installed.
    Please run npm install -g @vue/cli-upgrade and try again.
  </code></pre>
  
  <p>So, I've installed <strong>@vue/cli-upgrade</strong> and try vue upgrade again, but the message is repeating.</p>
  
  <pre><code>ueda@klingsor:~/ml$ sudo npm install -g @vue/cli-upgrade
  + @vue/cli-upgrade@3.12.1
  updated 1 package in 7.273s
  ueda@klingsor:~/ml$ sudo vue upgrade
  
    Command vue upgrade requires a global addon to be installed.
    Please run npm install -g @vue/cli-upgrade and try again.
  </code></pre>
  
  <p>Also, the version of vue cli has still remained as 3.4.1</p>
  
  <pre><code>ueda@klingsor:~/ml$ vue --version
  3.4.1
  </code></pre>
  
  <p>How can I upgrade my vue-cli to 4? Thank you for your suggestion!</p>
  
  <p>My environment is ubunto 14.04, and npm is version 6.13.7</p>
  
  <pre><code>ueda@klingsor:~/ml$ cat /etc/os-release 
  NAME="Ubuntu"
  VERSION="14.04.2 LTS, Trusty Tahr"
  </code></pre>
  
  <pre><code>ueda@klingsor:~/ml$ npm --version
  6.13.7```
  </code></pre>