title: Getting error only one sdist may be uploaded
body: <p>Why is this creating 2 tar.gz files, ‘
  <code>python setup.py sdist</code>?  I am trying to upload using 
  <code>twine upload -r pypitest dist/*.tar.gz</code> and i get error saying </p>
  
  <pre><code>HTTPError: 400 Client Error: Only one sdist may be uploaded per release. for url: https://test.pypi.org/legacy/
  ERROR: Job failed: exit code 1
  </code></pre>
  
  <p>Here is the full <a href="https://gitlab.com/sansupercool/git-maildiff/blob/master/setup.py" rel="noreferrer">setup.py</a></p>