Fix import error in script to convert faisreq roberta checkpoints

transformers/convert_roberta_original_pytorch_checkpoint_to_pytorch.py

@@ -23,12 +23,12 @@ import torch
 
 from fairseq.models.roberta import RobertaModel as FairseqRobertaModel
 from fairseq.modules import TransformerSentenceEncoderLayer
-from transformers import (BertConfig, BertEncoder,
+from transformers.modeling_bert import (BertConfig, BertEncoder,
                                         BertIntermediate, BertLayer,
                                         BertModel, BertOutput,
                                         BertSelfAttention,
                                         BertSelfOutput)
-from transformers import (RobertaEmbeddings,
+from transformers.modeling_roberta import (RobertaEmbeddings,
                                            RobertaForMaskedLM,
                                            RobertaForSequenceClassification,
                                            RobertaModel)