Update docker image to use schema2 manifest

[iemejia]

In the latest version of docker (19.03.8) when you pull this image you get the following warning so maybe worth the fix:

Image docker.io/ikatson/aceproxy:latest uses outdated schema1 manifest format.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/

Oh and before I forget thanks for making this image available!