Update ECR credential helper

[SoManyHs]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[SoManyHs]

Logs still write correctly to ~/.ecr/log/ecr-login.log:

time="2018-11-19T11:52:00-08:00" level=info msg="Pulling image" repository=xxxxxxxxx51.dkr.ecr.us-west-2.amazonaws.com/xray-daemon tag=
time="2018-11-19T11:52:01-08:00" level=info msg="Image pulled"
time="2018-11-19T11:54:25-08:00" level=debug msg="Getting images from ECR..."
time="2018-11-19T11:57:05-08:00" level=info msg="Getting AWS account ID..."
time="2018-11-19T11:57:06-08:00" level=debug msg="Getting authorization token..."
time="2018-11-19T11:57:06-08:00" level=debug msg="Checking file cache" registry=xxxxxxxxx51
time="2018-11-19T11:57:06-08:00" level=debug msg="Using cached token" registry=xxxxxxxxx51
time="2018-11-19T11:57:06-08:00" level=info msg="Tagging image" image=x-ray repository=xxxxxxxxx51..dkr.ecr.us-west-2.amazonaws.com/x-ray tag=
time="2018-11-19T11:57:06-08:00" level=fatal msg="Error executing 'push': unable to tag image: API error (404): No such image: x-ray:latest\n"

[SoManyHs]

Related to awslabs/amazon-ecr-credential-helper#127

[PettitWesley]

Approved despite my apprehensions about the numerology of this PR #666 #signofthebeast