When using the command apt-get update
sometimes your file just won't build. Most of the time this is due to the sources used by apt-get not being up-to-date.
The following RUN
command can be added if your image is based on debian/jessie
# UPDATE SOURCES
RUN printf "deb http://archive.debian.org/debian/ jessie main\ndeb-src http://archive.debian.org/debian/ jessie main\ndeb http://security.debian.org jessie/updates main\ndeb-src http://security.debian.org jessie/updates main" > /etc/apt/sources.list