When using 'podman push', for some reason the image manifest isn't 
accessible in the Docker Hub. This commit uses an image pushed by 
'docker':

docker pull am97/jekyll-indigo-build:latest
docker tag am97/jekyll-indigo-build:latest 
am97/jekyll-indigo-build:docker-20200401
docker push am97/jekyll-indigo-build:docker-20200401