title: Attempting push on git and receiving "could not read Username for 'https://github.com': terminal prompts disabled"
body: <p>I'm using Visual Studio, and the GitHub Extension. I am able to sign in, then clone my team's repository, and then pull changes successfully.</p>
  
  <p>When it comes time to push my changes back to remote, I get a blank command prompt appear on the screen briefly, and then the following errors in the output window:</p>
  
  <blockquote>
    <p>Error encountered while pushing to the remote repository: Git failed with a fatal error. </p>
    
    <p>fatal: AggregateException encountered. One or more errors occurred. </p>
    
    <p>error: cannot spawn askpass: No such file or directory </p>
    
    <p>fatal: could not read Username for '<a href="https://github.com" rel="noreferrer">https://github.com</a>': terminal prompts disabled</p>
  </blockquote>
  
  <p>EDIT: pushing via the command line works, as does pushing via the GitHub desktop application, just not within this extension.</p>
  
  <p>Any ideas why this might be happening? I can't see why it needs the Username given that I have signed into the extension.</p>