title: flake8 linter in Sublime Text stopped showing F841 assigned but never used warning
body: <p>As the title states, in Sublime Text 3.1.1 with flake8 3.5 for the following python code:</p>
  
  <pre><code>x = 1
  y = 2
  print(y)
  </code></pre>
  
  <p>I would expect x = 1 to be highlighted with F841 "local variable
  name is assigned to but never used" warning but it doesn't show up neither in the code nor in the linter gutter. There is nothing referencing code F841 in any of the linter settings files (no exclusions). Apart from this, linter appears to be working fine. I can obviously code without this, but it'd be nice to know what goes on here, so any suggestions would be appreciated. Thanks.</p>