Fix model parallel LM (#1358)

Summary: Pull Request resolved: fairinternal/fairseq-py#1358

Reviewed By: alexeib

Differential Revision: D24393064

Pulled By: myleott

fbshipit-source-id: ee88fd1e7b203d7df6b7a65d3b1b1469e8fe9b6e

Author: Myle Ott

fairseq/model_parallel/models/transformer_lm.py

@@ -22,6 +22,11 @@
 
 @register_model("model_parallel_transformer_lm")
 class ModelParallelTransformerLanguageModel(TransformerLanguageModel):
+
+    @staticmethod
+    def add_args(parser):
+        TransformerLanguageModel.add_args(parser)
+
     @classmethod
     def build_model(cls, args, task):
         """Build a new model instance."""