According to the ebuild found here: https://gitweb.gentoo.org/repo/gentoo.git/tree/app-emulation/docker/docker-1.13.1-r2.ebuild it has a new dependency on app-emulation/docker-runc, and the old dependency, >=app-emulation/containerd-0.2.5. However, app-emulation/containerd-0.2.5 is dependent on app-emulation/runc. app-emulation/docker-runc and app-emulation/runc block each other.
Please test with stable 17.03.1