No name 'AlbertMLMHead' in module 'transformers'
# 🌟 New model addition

## Model description

MLM model head
```
No name 'AlbertMLMHead' in module 'transformers'
```

## Open source status

* [x] the model implementation is available: 
```
class AlbertMLMHead(nn.Module):
    def __init__(self, config):
        super().__init__()

        self.LayerNorm = nn.LayerNorm(config.embedding_size)
        self.bias = nn.Parameter(torch.zeros(config.vocab_size))
        self.dense = nn.Linear(config.hidden_size, config.embedding_size)
        self.decoder = nn.Linear(config.embedding_size, config.vocab_size)
        self.activation = ACT2FN[config.hidden_act]

        # Need a link between the two variables so that the bias is correctly resized with `resize_token_embeddings`
        self.decoder.bias = self.bias

    def forward(self, hidden_states):
        hidden_states = self.dense(hidden_states)
        hidden_states = self.activation(hidden_states)
        hidden_states = self.LayerNorm(hidden_states)
        hidden_states = self.decoder(hidden_states)

        prediction_scores = hidden_states

        return prediction_scores


[DOCS]@add_start_docstrings(
    "Albert Model with a `language modeling` head on top.", ALBERT_START_DOCSTRING,
)
```
Include in the __initial__ file and make it available for use.

* [ ] the model weights are available: (give details)
* [ ] who are the authors: (mention them, if possible by @gh-username)

Hi, you can import it as such:
```py
from transformers.modeling_albert import AlbertMLMHead
```

It's not in the `__init.py__` as it's not a model but part of one.