type hints fixes

freqtrade/freqai/base_models/PyTorchModelTrainer.py

@@ -1,6 +1,7 @@
 import logging
 from pathlib import Path
 from typing import Dict
+from torch.optim import Optimizer
 
 import torch
 import torch.nn as nn
@@ -15,7 +16,7 @@ class PyTorchModelTrainer:
     def __init__(
             self,
             model: nn.Module,
-            optimizer: nn.Module,
+            optimizer: Optimizer,
             criterion: nn.Module,
             device: str,
             batch_size: int,