Crystal Ubuntu package does not install all required dependencies

Dockerfile

FROM ubuntu

MAINTAINER Andy Nicholson <andrew@anicholson.net>

RUN apt-get update && \
    apt-get install -y apt-transport-https && \
    apt-key adv --keyserver keys.gnupg.net --recv-keys 09617FD37CC06B54 && \
    echo "deb https://dist.crystal-lang.org/apt crystal main" > /etc/apt/sources.list.d/crystal.list && \
    apt-get update && \
    apt-get install -y crystal

RUN echo 'puts "WORKING!"' > /tmp/test.cr

RUN crystal build -o test /tmp/test.cr

ENTRYPOINT test