chapter14 activation issue in CBOW embedding ?

```
x = cbow_embedding(inputs)
x = layers.GlobalAveragePooling1D()(x)
outputs = layers.Dense(max_tokens, activation="sigmoid")(x)
```

should be 
```
x = cbow_embedding(inputs)
x = layers.GlobalAveragePooling1D()(x)
outputs = layers.Dense(max_tokens, activation="softmax")(x)
```