Fix bug from `transformer.ipynb` in `/experiments`

[A-baoYang]

Hi, thank you so much for open sourcing your project, it helps me a lot!! Here I just have one simple bug to report:

---

Source: 3rd code cell from notebook

• Original:

  outputs = Transformer(
  vocab_size, 
  model_dim, 
  n_heads=2, 
  encoder_stack=2,
  decoder_stack=2, 
  feed_forward_size=50
  )([encoder_inputs, decoder_inputs])

After ran the notebook and traced your code (deep_recommenders/keras/models/nlp/Transformer.py), the input of Transformer class object needs 2 parameters (encoder_inputs, decoder_inputs), it should not be a list.

• Revised:

  outputs = Transformer(
  vocab_size, 
  model_dim, 
  n_heads=2, 
  encoder_stack=2,
  decoder_stack=2, 
  feed_forward_size=50
  )(encoder_inputs, decoder_inputs)

[SharpCX]

We have fix the issues, thx.