title: git hook flake8: error: input not specified
body: <p>Flake8's <code>pre-commit</code> hook for git raises <code>flake8: error: input not specified</code> whenever I do git commit.</p>
  
  <p>The hook file is identical to the <a href="https://flake8.readthedocs.org/en/2.0/vcs.html#git-hook" rel="nofollow">official example</a> : </p>
  
  <pre><code>#!/usr/bin/python
  import sys
  from flake8.run import git_hook
  
  COMPLEXITY = 10
  STRICT = False
  
  if __name__ == '__main__':
      sys.exit(git_hook(complexity=COMPLEXITY, strict=STRICT, ignore='E501'))
  </code></pre>