title: Invalid parameter for sklearn estimator pipeline
body: <p>I am implementing an example from the O'Reilly book "<em>Introduction to Machine Learning with Python</em>", using Python 2.7 and sklearn 0.16.</p>
  
  <p>The code I am using:</p>
  
  <pre><code>pipe = make_pipeline(TfidfVectorizer(), 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(X_train, y_train)
  print("Best cross-validation score: {:.2f}".format(grid.best_score_))
  </code></pre>
  
  <p>The error being returned boils down to:</p>
  
  <pre><code>ValueError: Invalid parameter logisticregression_C for estimator Pipeline
  </code></pre>
  
  <p>Is this an error related to using Make_pipeline from v.0.16? What is causing this error?</p>