docker build -t sourcekit-builder:311 https://github.com/norio-nomura/docker-sourcekit-builder.git
docker run --rm sourcekit-builder:311 context | docker build -t norionomura/sourcekit:311 -
docker run --rm sourcekit-builder:311 context | tar xv - "*.tar.gz"
x ./swift-3.1.1-RELEASE-<hash of commit in swift-dev>-with-sourcekit.tar.gz