fix refrence bug

In torch==1.5, the import of the API has changed. Although it does not interrupt the operation of the program, it seems to me to be an implicit error and may throw an exception in later versions.

detect.py

@@ -1,5 +1,7 @@
 import argparse
 
+import torch.backends.cudnn as cudnn
+
 from utils.datasets import *
 from utils.utils import *
 
@@ -36,7 +38,7 @@ def detect(save_img=False):
     vid_path, vid_writer = None, None
     if webcam:
         view_img = True
-        torch.backends.cudnn.benchmark = True  # set True to speed up constant image size inference
+        cudnn.benchmark = True  # set True to speed up constant image size inference
         dataset = LoadStreams(source, img_size=imgsz)
     else:
         save_img = True

train.py

@@ -4,6 +4,7 @@ import torch.distributed as dist
 import torch.nn.functional as F
 import torch.optim as optim
 import torch.optim.lr_scheduler as lr_scheduler
+import torch.utils.data
 from torch.utils.tensorboard import SummaryWriter
 
 import test  # import test.py to get mAP after each epoch