Fix Tensorboard Init (#763)

Summary:
Fix the mismatching between the parameter fed into `SummaryWriter` and the API of the latest [tensorboardX](https://github.com/lanpa/tensorboardX/blob/3e35c9b5f85e8ceb0294532d9eb772341a04c097/tensorboardX/writer.py#L192), i.e. "log_dir" -> "logdir".
Pull Request resolved: https://github.com/pytorch/fairseq/pull/763

Differential Revision: D15547192

Pulled By: myleott

fbshipit-source-id: c51b88da5ec589fb8ca5b4876bc229efeb7bf494

fairseq/progress_bar.py

@@ -225,7 +225,7 @@ class tensorboard_log_wrapper(progress_bar):
             self._writers = {}
         except ImportError:
             print("tensorboard or required dependencies not found, "
-                  "please see README for using tensorboard.")
+                  "please see README for using tensorboard. (e.g. pip install tensorboardX)")
             self.SummaryWriter = None
 
     def _writer(self, key):
@@ -233,7 +233,7 @@ class tensorboard_log_wrapper(progress_bar):
             return None
         if key not in self._writers:
             self._writers[key] = self.SummaryWriter(
-                log_dir=os.path.join(self.tensorboard_logdir, key),
+                os.path.join(self.tensorboard_logdir, key),
             )
             self._writers[key].add_text('args', str(vars(self.args)))
             self._writers[key].add_text('sys.argv', " ".join(sys.argv))