small fixes

model.py

@@ -14,10 +14,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from huggingface_hub import hf_hub_download
-from functools import lru_cache
 import os
+from functools import lru_cache
+from typing import Union
+
 import torchaudio
+from huggingface_hub import hf_hub_download
 
 os.system(
     "cp -v /home/user/.local/lib/python3.8/site-packages/k2/lib/*.so /home/user/.local/lib/python3.8/site-packages/sherpa/lib/"
@@ -26,7 +28,6 @@ os.system(
 import k2
 import sherpa
 
-
 sample_rate = 16000