Please allow --privileged flag to build multiarch docker images.
According to this article, it is possible with Github + Travis :
http://blog.hypriot.com/post/setup-simple-ci-pipeline-for-arm-images/

Register qemu-*-static for all supported processors except the current one
docker run --rm --privileged multiarch/qemu-user-static:register

Currently, the following error is return when running the pipeline:

• docker run --rm --privileged multiarch/qemu-user-static:register --reset
  docker: Error response from daemon: authorization denied by plugin pipelines: Command not supported.
  See 'docker run --help'.

Thanks