title: ModuleNotFoundError: No module named 'sklearn.externals.six'
body: <p>I keep getting the error</p>
  <pre><code>ModuleNotFoundError: No module named 'sklearn.externals.six'
  </code></pre>
  <p>when running the code below:</p>
  <pre><code>from sklearn.datasets import load_iris
  from sklearn.model_selection import train_test_split
  import pandas as pd
  import mglearn
  import numpy as np
  from IPython.display import display
  import matplotlib as pl
  import sklearn
  
  iris_dataset = load_iris()
  X_train, X_test, y_train, y_test = train_test_split(iris_dataset['data'], iris_dataset['target'], random_state=0)
  iris_dataframe = pd.DataFrame(X_train, columns=iris_dataset.feature_names)
  pd.plotting.scatter_matrix(iris_dataframe, c=y_train, figsize=(15, 15), marker='o', hist_kwds={'bins':20}, s=60, alpha=.8, cmap=mglearn.cm3)
  </code></pre>
  <p>Is there a module I haven't imported or installed?</p>