The previous syntax ended up executing:

  docker run -d hypothesis s3://cdn.hypothes.is nickstenning/s3-npm-publish

So `hypothesis` was interpreted as the Docker image name instead of an
argument. Passing the args as the second ('command') argument to
`Image.withRun` results in the correct command being executed:

  docker run -d nickstenning/s3-npm-publish hypothesis s3://cdn.hypothes.is