fix resize_token_embeddings to accept padding_idx for xlm-roberta models
When resize_token_embedding there is no option for padding_idx 
and it leads to the wrong embedding for xlm-roberta models 
which needs embedding to have padding_idx as 1 not 0.

I fixed issue by adding option for padding_idx and considered padding_idx as None (which is 0 as default) for compatibility for other types of transformers models.