title: ModuleNotFoundError: No module named 'allennlp.common'
body: <p>I am getting this error while importing allennlp,</p>
  
  <pre><code>from allennlp.common.util import sanitize
  ModuleNotFoundError: No module named 'allennlp.common'
  (venv-kbs) administrator@NLR:~/aman/Project$ python
  Python 3.6.3 (default, Oct  6 2017, 00:00:00)
  [GCC 4.8.4] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; import allennlp
  &gt;&gt;&gt; from allennlp.common.util import sanitize
  Traceback (most recent call last):
  File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  ModuleNotFoundError: No module named 'allennlp.common'
  </code></pre>
  
  <p>My allennlp version is 0.2.1 and even trying to update to 0.4.1 it gives the same error. </p>
  
  <p>TIA</p>