unable to install anything in Dockerfile

Docker newbie here, I want to create a new image based on another image I pulled from Dockerhub which by itself works great but I wanted to add some tools to it.
My Dockerfile is very small and it already fails:

FROM aunsbjerg/docker-kinetis-design-studio

RUN echo "hello world!"
RUN apt-get update && apt-get install -y apt-utils

The hello world line by itself seems to work fine but as soon as I try to install any program, it fails with:

The command '/bin/sh -c apt-get update && apt-get install -y apt-utils' returned a non-zero code: 100

Why is this and how do I get past it?

sed -i 's/udevadm/#udevadm/' /var/lib/dpkg/info/kinetis-design-studio.postinst && dpkg --configure --pending