text: Title: There is no config.json in pre-trained BERT models by DeepPavlov
  Body: BERT pre-trained models from http://docs.deeppavlov.ai/en/master/features/pretrained_vectors.html#bert have `bert_config.json` instead of `config.json`. This leads to errors when these models are used with HuggingFace Transformers:
  
  ```python
  from transformers import AutoTokenizer
  t = AutoTokenizer.from_pretrained("./conversational_cased_L-12_H-768_A-12_v1")
  ```
  
  ```
  OSError                                   Traceback (most recent call last)
  <ipython-input-2-1a3f920b5ef3> in <module>
  ----> 1 t = AutoTokenizer.from_pretrained("/home/yurakuratov/.deeppavlov/downloads/bert_models/conversational_cased_L-12_H-768_A-12_v1")
  
  ~/anaconda3/envs/dp_tf1.15/lib/python3.7/site-packages/transformers/tokenization_auto.py in from_pretrained(cls, pretrained_model_name_or_path, *inputs, **kwargs)
      184         config = kwargs.pop("config", None)
      185         if not isinstance(config, PretrainedConfig):
  --> 186             config = AutoConfig.from_pretrained(pretrained_model_name_or_path, **kwargs)
      187
      188         if "bert-base-japanese" in pretrained_model_name_or_path:
  
  ~/anaconda3/envs/dp_tf1.15/lib/python3.7/site-packages/transformers/configuration_auto.py in from_pretrained(cls, pretrained_model_name_or_path, **kwargs)
      185         """
      186         config_dict, _ = PretrainedConfig.get_config_dict(
  --> 187             pretrained_model_name_or_path, pretrained_config_archive_map=ALL_PRETRAINED_CONFIG_ARCHIVE_MAP, **kwargs
      188         )
      189
  
  ~/anaconda3/envs/dp_tf1.15/lib/python3.7/site-packages/transformers/configuration_utils.py in get_config_dict(cls, pretrained_model_name_or_path, pretrained_config_archive_map, **kwargs)
      268                     )
      269                 )
  --> 270             raise EnvironmentError(msg)
      271
      272         except json.JSONDecodeError:
  
  OSError: Can't load '/home/yurakuratov/.deeppavlov/downloads/bert_models/conversational_cased_L-12_H-768_A-12_v1'. Make sure that:
  
  - '/home/yurakuratov/.deeppavlov/downloads/bert_models/conversational_cased_L-12_H-768_A-12_v1' is a correct model identifier listed on 'https://huggingface.co/models'
  
  - or '/home/yurakuratov/.deeppavlov/downloads/bert_models/conversational_cased_L-12_H-768_A-12_v1' is the correct path to a directory containing a 'config.json' file
  ```
  
  Renaming `bert_config.json` to `config.json` should solve the problem.