Docker image link in README.md leads to an unexpected website

[kaftanski]

The link for the docker image in the README now leads to a dubious looking website:

https://github.com/BioMedIA/MIRTK/blob/973ce2fe3f9508dec68892dbf97cca39067aa3d6/README.md?plain=1#L6

The microbadger domain seems to be no longer operated by the intended provider.