PyTorch 1.6.0 compatability updates

detect.py

@@ -154,7 +154,7 @@ if __name__ == '__main__':
 
     with torch.no_grad():
         if opt.update:  # update all models (to fix SourceChangeWarning)
-            for opt.weights in ['yolov5s.pt', 'yolov5m.pt', 'yolov5l.pt', 'yolov5x.pt', 'yolov3-spp.pt']:
+            for opt.weights in ['yolov5s.pt', 'yolov5m.pt', 'yolov5l.pt', 'yolov5x.pt']:
                 detect()
                 strip_optimizer(opt.weights)
         else: