Add ca-certificates to the packages installed for the haproxy/syslogsrv build (#18)

This required to pull dependencies from the internet, as recommended in the README.

The development environment we have internally provides a container that is *very nearly* the same as the usual ubuntu image,
but not quite the same, in particular it appears to have this pre-installed which explains how we missed this until now.

Author: jacquesh

Dockerfile

@@ -51,7 +51,7 @@ ARG git_proxy
 WORKDIR /workspace
 RUN <<EOF
     apt-get update
-    apt-get install -y --no-install-recommends cmake g++ make git
+    apt-get install -y --no-install-recommends cmake g++ make git ca-certificates
     apt-get clean
     rm -rf /var/lib/apt/lists/*  # Remove the apt cache lists to keep image size down
 EOF
@@ -72,7 +72,7 @@ WORKDIR /workspace
 STOPSIGNAL SIGUSR1
 RUN <<EOF
     apt-get update
-    apt-get install -y --no-install-recommends cmake g++ make git lua5.3 lua5.3-dev libpcre3-dev libssl-dev lua-penlight
+    apt-get install -y --no-install-recommends cmake g++ make git lua5.3 lua5.3-dev libpcre3-dev libssl-dev lua-penlight ca-certificates
     apt-get clean
     rm -rf /var/lib/apt/lists/*  # Remove the apt cache lists to keep image size down
     git config --global http.proxy "${git_proxy}"