title: How to specify a specific github repo version in requirements.txt?
body: <p>I want to be able to install a specific version of a github repo. I followed the instructions given <a href="https://stackoverflow.com/questions/16584552/how-to-state-in-requirements-txt-a-direct-github-source">here</a> and my file <code>requirements.txt</code> looks as follows:</p>
  
  <pre><code>git://github.com/twoolie/NBT@f9e892e
  </code></pre>
  
  <p>I also tried the following versions:</p>
  
  <pre><code>git+git://github.com/twoolie/NBT@f9e892e
  git+git://github.com/twoolie/NBT.git@f9e892e
  git://github.com/twoolie/NBT.git@f9e892e
  </code></pre>
  
  <p>but in every case when I try to install the actual package, which requires the repository <code>NBT</code> from commit hash f9e892e, I get the error message</p>
  
  <pre><code>error in PyBlock setup command: 'install_requires' must be a string or list of strings containing valid project/version requirement specifiers; Invalid requirement, parse error at "'://githu'"
  </code></pre>
  
  <p>So how to do it correctly?</p>