Update chainerx_cc/examples/mnist_py/train_mnist.py
Update chainerx_cc/examples/mnist_py/train_mnist.py

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Co-Authored-By: Guriido <9b68ad2941a168ea9ed8c4afde236ccab087ec32@laposte.net>
wkentaro/chainer,niboshi/chainer,wkentaro/chainer,chainer/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,hvy/chainer,okuta/chainer,hvy/chainer,okuta/chainer,keisuke-umezawa/chainer,wkentaro/chainer,niboshi/chainer,pfnet/chainer,keisuke-umezawa/chainer,okuta/chainer,niboshi/chainer,hvy/chainer,hvy/chainer,tkerola/chainer,chainer/chainer,wkentaro/chainer,niboshi/chainer,chainer/chainer,chainer/chainer,okuta/chainer