title: Changing https-address of submodules in .git/config to ssh-address
body: <p>I need to use ssh forwarding-agent to enable git cloning on remote servers. The repository has submodules which were originally added with their <code>https</code> addresses. In order for forwarding agent to work, I think I need to change those addresses to their corresponding <code>ssh</code> address. </p>
  
  <p>Will changing these addresses in <code>.git/config</code> solve my problem? </p>