Update torchscript.rst

Import fixed to pytorch_transformers else torchscript flag can't be used.

docs/source/torchscript.rst

@@ -74,7 +74,7 @@ according to a ``BertConfig`` class and then saved to disk under the filename ``
 
 .. code-block:: python
 
-    from pytorch_pretrained_bert import BertModel, BertTokenizer, BertConfig
+    from pytorch_transformers import BertModel, BertTokenizer, BertConfig
     import torch
 
     enc = BertTokenizer.from_pretrained("bert-base-uncased")
@@ -129,4 +129,4 @@ Using the traced model for inference is as simple as using its ``__call__`` dund
 
 .. code-block:: python
 
-    traced_model(tokens_tensor, segments_tensors)
+    traced_model(tokens_tensor, segments_tensors)