title: pip - Installing specific package version does not work
body: <p>I was trying to install a library (<code>allennlp</code>) via <code>pip3</code>. But it complained about the PyTorch version. While <code>allennlp</code> requires <code>torch=0.4.0</code> I have <code>torch=0.4.1</code>:</p>
  
  <pre><code>...
  Collecting torch==0.4.0 (from allennlp)
    Could not find a version that satisfies the requirement torch==0.4.0 (from allennlp) (from versions: 0.1.2, 0.1.2.post1, 0.4.1)
  No matching distribution found for torch==0.4.0 (from allennlp)
  </code></pre>
  
  <p><em>Also manually install:</em></p>
  
  <pre><code>pip3 install torch==0.4.0
  </code></pre>
  
  <p><em>Doesn't work either:</em></p>
  
  <pre><code>  Could not find a version that satisfies the requirement torch==0.4.0 (from versions: 0.1.2, 0.1.2.post1, 0.4.1)
  No matching distribution found for torch==0.4.0
  </code></pre>
  
  <p>Same for other versions.</p>
  
  <p>Python is version <code>Python 3.7.0</code> installed via <code>brew</code> on Mac OS.</p>
  
  <p>I remember that some time ago I was able to switch between version <code>0.4.0</code> and <code>0.3.1</code> by using <code>pip3 install torch==0.X.X</code>.</p>
  
  <p>How do I solve this?</p>