fix torch env typo

[kuizhiqing]

What this PR does / why we need it:
There is a wrong env set for pytorch.

PET_N_PROC_PER_NODE should be PET_NPROC_PER_NODE according to
https://github.com/pytorch/pytorch/blob/master/torch/distributed/argparse_util.py#L12-L57

Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

• [*] Docs included if any changes are user facing

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Hi @kuizhiqing. Thanks for your PR.

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[gaocegege]

/lgtm
/approve

Thanks for your contribution! 🎉 👍

[gaocegege]

/ok-to-test

[gaocegege]

Please sign the CLA

[Arhell]

/lgtm

[coveralls]

Pull Request Test Coverage Report for Build 2147091797

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 37.172%

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Totals
Change from base Build 2063930985:	0.0%
Covered Lines:	2308
Relevant Lines:	6209

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💛 - Coveralls

[kuizhiqing]

/retest

[terrytangyuan]

Thanks!

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gaocegege, kuizhiqing, terrytangyuan

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[gaocegege]

/retest

[gaocegege]

Thanks for your contribution! 🎉 👍