title: composer git clone --mirror failed
body: <p>I have private repo on stash and access with ssh key. I configured hostname, port, ssh file (_rsa) on <code>.ssh/config file</code>. Later I execute <code>git clone ssh://git@stash..</code> command on terminal. It works. When I execute <code>composer update vendor/repo:dev-master</code> command on terminal, This command failed and gives following error:</p>
  
  <blockquote>
    <p>Repository not found<br>
    The requested repository does not exist, or you do not have permission
    to access it.<br>
    fatal: Could not read from remote repository.<br>
    Please make sure you have the correct access rights<br>
    and the repository exists.</p>
  </blockquote>