Use python3 super syntax (pytorch#976)

minor improvement - only python3 is supported by Torch 1.5, so we can use newer, shorter syntax.

Co-authored-by: holly1238 <[email protected]>

Author: ikamensh

beginner_source/blitz/cifar10_tutorial.py

@@ -125,7 +125,7 @@ def imshow(img):
 
 class Net(nn.Module):
     def __init__(self):
-        super(Net, self).__init__()
+        super().__init__()
         self.conv1 = nn.Conv2d(3, 6, 5)
         self.pool = nn.MaxPool2d(2, 2)
         self.conv2 = nn.Conv2d(6, 16, 5)