title: firebase version is not updating through <npm install -g firebase-tools>
body: <p>i am windows user and trying to update firebase version using 
  <strong>npm install -g firebase-tools</strong> but when i run <strong>firebase --version</strong>
  it shows the same version. 
  I also run npm uninstall <strong>firebase --save</strong> and check <strong>firebase --version</strong> it shows same. 
  what should i do to update my firebase version?</p>