Can't GPT-2 set special_tokens? (or unk tokens)
## ❓ Questions & Help

<!-- A clear and concise description of the question. -->
In GPT, we can set special tokens. (I also did it branch 0.6.2)
https://github.com/huggingface/pytorch-transformers/blob/v1.0.0/pytorch_transformers/modeling_openai.py

But, in GPT-2, It seems like no way to add special tokens.
https://github.com/huggingface/pytorch-transformers/blob/b33a385091de604afb566155ec03329b84c96926/pytorch_transformers/modeling_gpt2.py#L619

I also saw #994. They said it's impossible. 
It it true? and do you have any plan to add it?
I also saw #468. It will be probably added soon.
But, If someone informs new information about this, I'll thank for that.<|||||>Passing them like so works for me:

`GPT2Tokenizer.from_pretrained(args.model_name, unk_token="<|endoftext|>")`

You can all pass a list to `tokenizer.add_tokens`, then call `model.resize_token_embeddings(len(tokenizer))`.<|||||>@aburkard  Thank you so much!!!! I'll try it.
<|||||>Hi, in GPT-2 there wasn't the option at first but we've added it down the line. It is available if you compile this repo from source from the master branch, or you can wait for the version 1.1 which should drop sometimes this week. In this version you're able to add special tokens to GPT-2.<|||||>Release 1.1.0 is here :-)<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
