title: Conflicting default and custom paths for nltk_data
body: <p>I understand that there should be two different directories for nltk_data: one for the default download and another one for the user's custom files. </p>
  
  <p>In my macOS setup I have manually checked that all the default data packages are in <code>/usr/local/share/nltk_data</code>, and that is the outcome of <code>next(p for p in nltk.data.path if os.path.exists(p))</code>. </p>
  
  <p>However, when I try to download another default package it doesn't go to that directory, but to <code>/Users/macbook/nltk_data</code>, where I understant that only my custom files should be. And testing the instalation for the default <code>nltk.corpus.brown.words()</code> fails because it looks for it in my custom path: <code>'No such file or directory: '/Users/macbook/nltk_data/corpora/brown/ca01'</code></p>
  
  <p>I am using Python 3.6.3, conda 4.4.8, and the outcome of <code>print(nltk.data.path)</code>is</p>
  
  <blockquote>
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      <blockquote>
        <p>['/Users/macbook/nltk_data', '/usr/share/nltk_data', '/usr/local/share/nltk_data', '/usr/lib/nltk_data', '/usr/local/lib/nltk_data', '/Users/macbook/anaconda3/nltk_data', '/Users/macbook/anaconda3/lib/nltk_data', '/usr/local/share/nltk_data']</p>
      </blockquote>
    </blockquote>
  </blockquote>