Build warning when using dnd

[pdiazvargas]

Actual

When using juniper to build artifacts in a gitlab runner using a docker in docker dnd image, I get the following warning:

time="2019-03-22T03:55:20Z" level=error msg="Error parsing the serverURL" error="docker-credential-ecr-login can only be used with Amazon Elastic Container Registry." serverURL="https://index.docker.io/v1/"
build-python3.6: Pulling from lambci/lambda
Pulling benchmark-api-lambda (lambci/lambda:build-python3.7)...
time="2019-03-22T03:56:07Z" level=error msg="Error parsing the serverURL" error="docker-credential-ecr-login can only be used with Amazon Elastic Container Registry." serverURL="https://index.docker.io/v1/"

Gitlab configuration:

build:
  image: docker:latest
  services:
    - docker:dind
  stage: build
  when: on_success
  dependencies: []
  before_script:
    - time apk add --no-cache --update python3
    - time pip3 install --upgrade pip setuptools docker-compose
    - rm -rf /tmp/*
    - rm -rf /var/cache/apk/*
  script:
    - juni build

The artifacts do get built, but the warning is incovenient. There seems to be a related problem defined in this issue: awslabs/amazon-ecr-credential-helper#76

Expected

Either document and implement a way to address this message when building or document for the sake for awareness.