title: beautifulsoup, html5lib: module object has no attribute _base
body: <p>When I updated my packages I have this new error:</p>
  
  <pre><code>class TreeBuilderForHtml5lib(html5lib.treebuilders._base.TreeBuilder):
  AttributeError: 'module' object has no attribute '_base'
  </code></pre>
  
  <p>I tried to update <code>beautifulsoup</code>, with no more result. How can I fix that?</p>