Outdated Dockerfile format

[emicklei]

Hi,

Thank you for providing this setup.
I did get a warning when building it:

Image docker.io/mkboudreau/go-present:latest uses outdated schema1 manifest format. Please upgrade to a schema2 image for better future compatibility. More information at https://docs.docker.com/registry/spec/deprecated-schema-v1/

[mkboudreau]

Updated