added cache_dir option in from_pretrained

pytorch_pretrained_bert/modeling.py

@@ -443,7 +443,7 @@ class PreTrainedBertModel(nn.Module):
             module.bias.data.zero_()
 
     @classmethod
-    def from_pretrained(cls, pretrained_model_name, *inputs, **kwargs):
+    def from_pretrained(cls, pretrained_model_name, cache_dir=None, *inputs, **kwargs):
         """
         Instantiate a PreTrainedBertModel from a pre-trained model file.
         Download and cache the pre-trained model file if needed.
@@ -468,7 +468,7 @@ class PreTrainedBertModel(nn.Module):
             archive_file = pretrained_model_name
         # redirect to the cache, if necessary
         try:
-            resolved_archive_file = cached_path(archive_file)
+            resolved_archive_file = cached_path(archive_file, cache_dir=cache_dir)
         except FileNotFoundError:
             logger.error(
                 "Model name '{}' was not found in model name list ({}). "