Fix arg key for `dataset_name` in `create_model_card` (#158)

Fix arg key for `dataset_name`

The example training script was changed in #152, but not
`create_model_card`.

src/diffusers/hub_utils.py

@@ -168,13 +168,13 @@ def create_model_card(args, model_name):
             license="apache-2.0",
             library_name="diffusers",
             tags=[],
-            datasets=args.dataset,
+            datasets=args.dataset_name,
             metrics=[],
         ),
         template_path=MODEL_CARD_TEMPLATE_PATH,
         model_name=model_name,
         repo_name=repo_name,
-        dataset_name=args.dataset if hasattr(args, "dataset") else None,
+        dataset_name=args.dataset_name if hasattr(args, "dataset_name") else None,
         learning_rate=args.learning_rate,
         train_batch_size=args.train_batch_size,
         eval_batch_size=args.eval_batch_size,