title: I can't add optimizer parameter in gridsearch
body: <pre><code>from keras.wrappers.scikit_learn import KerasClassifier
  from sklearn.model_selection import GridSearchCV
  def build_classifier():
    classifier = Sequential()
    classifier.add(Dense(units = 6 , init='uniform' , activation= 'relu'))
    classifier.add(Dense(units = 6 , init='uniform' , activation= 'relu'))
    classifier.add(Dense(units = 1 , init='uniform' , activation= 'sigmoid'))
    classifier.compile(optimizer='adam' , loss = 'binary_crossentropy' , 
    metrics=['accuracy'])
    return classifier
  KC = KerasClassifier(build_fn=build_classifier)
  parameters = {'batch_size' : [25,32],
            'epochs' : [100,500],
            'optimizer':['adam','rmsprop']}
  grid_search = GridSearchCV(estimator=KC , 
  param_grid=parameters,scoring='accuracy',cv=10)
  grid_search.fit(X_train,y_train)
  </code></pre>
  
  <p>I wanna test the model with different optimizer. But I can't seem to add optimizer in grid search. Whenever I run the program, it shows error regarding to fitting the training set.</p>
  
  <p>ValueError: optimizer is not a legal parameter</p>