Fix repo name env

[jose5918]

FIxes a typo in the getenv for MASTER_REPO_NAME

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This change is 

[k8s-ci-robot]

Hi @jose5918. Thanks for your PR.

I'm waiting for a kubernetes or tensorflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[coveralls]

Coverage remained the same at 31.746% when pulling eabc780 on jose5918:fix-env-typo into 4220361 on tensorflow:master.

[coveralls]

Coverage remained the same at 31.746% when pulling eabc780 on jose5918:fix-env-typo into 4220361 on tensorflow:master.

[jlewi]

/ok-to-test