title: ImportError: cannot import name cross_validation
body: <p>I cannot import the cross_validation from sklearn library; I use sklearn version 0.20.0</p>
  
  <pre><code>from sklearn import cross_validation
  </code></pre>
  
  <p>later in the code:</p>
  
  <pre><code>features_train, features_test, labels_train, labels_test = cross_validation.train_test_split(word_data, authors, test_size=0.1, random_state=42)
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "D:\me\M.Sc\Udacity_ML_course\ud120-projects-  master\naive_bayes\nb_author_id.py", line 16, in &lt;module&gt;
      from email_preprocess import preprocess
    File "../tools/email_preprocess.py", line 8, in &lt;module&gt;
      from sklearn import cross_validation
  ImportError: cannot import name cross_validation
  </code></pre>