title: Git submodules: specify a specific SHA?
body: <p>I'm referencing a git submodule in my project, and now need to reference a specific SHA in the target git repo.</p>
  
  <pre><code># .gitmodules
  [submodule "vendor/plugins/ssl_requirement"]
    path = vendor/plugins/ssl_requirement
    url = git://github.com/retr0h/ssl_requirement.git
  </code></pre>
  
  <p>The SHA I want is <code>bc96ad96407a72a60e0542cf3b0cecc6ff9e278e</code>.</p>