MNT update import for keras

Author: glemaitre

doc/miscellaneous.rst

@@ -136,7 +136,7 @@ calling ``fit_generator`` method to train the model. To illustrate, we will
 define a logistic regression model::
 
   >>> import keras
-  >>> y = keras.utils.to_categorical(y, 3)
+  >>> y = keras.utils.np_utils.to_categorical(y, 3)
   >>> model = keras.Sequential()
   >>> model.add(keras.layers.Dense(y.shape[1], input_dim=X.shape[1],
   ...                              activation='softmax'))

imblearn/keras/tests/test_generator.py

@@ -8,7 +8,7 @@
 keras = pytest.importorskip("keras")
 from keras.models import Sequential  # noqa: E402
 from keras.layers import Dense  # noqa: E402
-from keras.utils import to_categorical  # noqa: E402
+from keras.utils.np_utils import to_categorical  # noqa: E402
 
 from imblearn.datasets import make_imbalance  # noqa: E402
 from imblearn.under_sampling import ClusterCentroids  # noqa: E402