fix checking push permissions by http

[frostmourner]

My registry is harbor by http. When I build image, error occurred on function CheckPushPermissions. The error is as follows：
error checking push permissions -- make sure you entered the correct tag name, and that you are authenticated correctly, and try again: checking push permission for "registry.paas/library/test:v0.5": Get https://registry.paas/v2/: dial tcp 10.142.114.130:443: connect: connection refused

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[priyawadhwa]

Hey @frostmourner -- #685 was just merged which should fix this issue. I'm going to go ahead and close this PR, but gcr.io/kaniko-project/executor: 51734fc3a33e04f113487853d118608ba6ff2b81 should incorporate this change until we get the next release out.