[fix] fix training and export error (#81)

wekws/bin/export_onnx.py

@@ -17,6 +17,7 @@ import argparse
 import torch
 import yaml
 
+import onnx
 import onnxruntime as ort
 
 from wekws.model.kws_model import init_model

wekws/model/kws_model.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import sys
-from typing import Optional
+from typing import Optional, Tuple
 
 import torch
 import torch.nn as nn