Typo: unused `loss_fn` in last cell of lesson4-mnist_sgd.ipynb

This error is probably without any consequence, but why not correct it?

In the very last cell of the notebook lesson4-mnist_sgd.ipynb,

loss_fn = nn.NLLLoss()

is never used, and instead a previous


object is used.

And losses.append(loss) should be replaced with losses.append(l), as in previous parts of the notebook.

Alternatively, keep loss_fn and make the appropriate changes inside the loop.