title: AttributeError: 'GridSearchCV' object has no attribute 'cv_results_'
body: <p>I try to apply this code :</p>
  
  <pre><code>pipe = make_pipeline(TfidfVectorizer(min_df=5), LogisticRegression())
  param_grid = {'logisticregression__C': [ 0.001, 0.01, 0.1, 1, 10, 100],
                "tfidfvectorizer__ngram_range": [(1, 1),(1, 2),(1, 3)]} 
  
  grid = GridSearchCV(pipe, param_grid, cv=5)
  grid.fit(text_train, Y_train)
  
  scores = grid.cv_results_['mean_test_score'].reshape(-1, 3).T
  # visualize heat map
  heatmap = mglearn.tools.heatmap(
  scores, xlabel="C", ylabel="ngram_range", cmap="viridis", fmt="%.3f",
  xticklabels=param_grid['logisticregression__C'],
  yticklabels=param_grid['tfidfvectorizer__ngram_range'])
  plt.colorbar(heatmap)
  </code></pre>
  
  <p>But I have this error :</p>
  
  <pre><code>AttributeError: 'GridSearchCV' object has no attribute 'cv_results_'
  </code></pre>