3.5-classifying-movie-reviews.ipynb 執行時會遇到 KeyError: 'acc', 'val_acc'

原書ch3 在 github 中的 3.5-classifying-movie-reviews.ipynb 中執行到：

import matplotlib.pyplot as plt
acc = history.history['acc']
val_acc = history.history['val_acc']

時會遇到兩個：
KeyError: 'acc'
KeyError: 'val_acc'

需修改爲：
acc = history.history['binary_accuracy']
val_acc = history.history['val_binary_accuracy']