docker build fails when runc is not the default runtime

[SvenDowideit]

I tried to build an rancher/os-kernel, and it dies with

Sending build context to Docker daemon  5.303MB
Step 1/31 : FROM ubuntu:16.04
 ---> 00fd29ccc6f1
Step 2/31 : RUN apt-get update     && apt-get install -y build-essential wget libncurses5-dev unzip bc curl python rsync ccache git vim libssl-dev kmod gnupg2 locales
 ---> Running in 0ab903400076
shim error: json: cannot unmarshal array into Go struct field processState.capabilities of type specs.LinuxCapabilities
time="2017-12-19T20:18:10+10:00" level=fatal msg="exit status 1" 
sven@t440s ~/go/src/github.com/rancher/os-kernel $