Dockerfile: clean after first apt-get round
This reduces the size of the image.
@@ -10,7 +10,8 @@ RUN apt-get -qq update && \
apt-get -qq -y --no-install-recommends install \
ca-certificates \
gnupg \
- software-properties-common > /dev/null
+ software-properties-common > /dev/null && \
+ apt-get -qq clean
RUN apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF && \
echo "deb http://download.mono-project.com/repo/ubuntu stable-focal main" | tee /etc/apt/sources.list.d/mono-official-stable.list && \
