Update nn_tutorial.py (#3173) #3507

Job	Run time
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	10m 39s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	48m 55s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	17m 16s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	29m 39s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	18m 15s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	16m 17s
pytorch_tutorial_build_worker (7, 15, linux.4xlarge.nvidia.gpu)	18m 15s
pytorch_tutorial_build_worker (8, 15, linux.4xlarge.nvidia.gpu)	12m 14s
pytorch_tutorial_build_worker (9, 15, linux.4xlarge.nvidia.gpu)	17m 43s
pytorch_tutorial_build_worker (10, 15, linux.4xlarge.nvidia.gpu)	13m 39s
pytorch_tutorial_build_worker (11, 15, linux.4xlarge.nvidia.gpu)	13m 19s
pytorch_tutorial_build_worker (12, 15, linux.4xlarge.nvidia.gpu)	27m 58s
pytorch_tutorial_build_worker (13, 15, linux.4xlarge.nvidia.gpu)	31m 6s
pytorch_tutorial_build_worker (14, 15, linux.4xlarge.nvidia.gpu)	32m 49s
pytorch_tutorial_build_worker (15, 15, linux.4xlarge.nvidia.gpu)	23m 49s
pytorch_tutorial_build_manager	18m 32s
	5h 50m 25s

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