title: git clone failed to begin relaying via HTTP
body: <p>When Using git clone, I come into an error.
  Here is the command and the error information.</p>
  
  <pre><code>[user@linux]$ git clone git@github.com:username/repertory.git
  FATAL: failed to begin relaying via HTTP.
  ssh_exchange_identification: Connection closed by remote host
  fatal: Could not read from remote repository.
  
  Please make sure you have the correct access rights and the repository exists.
  </code></pre>
  
  <p>Except for git@github, git clone https://...... and git clone git://...... works well. So i guess there is something wrong with ssh protocal, then i checked ssh.</p>
  
  <pre><code>[user@linux]$ ssh -T git@github.com
  Hi username! You've successfully authenticated, but GitHub does not provide shell access.
  </code></pre>
  
  <p>It seems that I can connect to github through ssh protocol properly. But what's wrong with git clone through ssh?</p>