docker: Install netcat since wait_for uses it

Without nc installed, wait_for will always time out since running nc will
fail, which wait_for doesn't distinguish from nc being unable to connect to
the target host

Author: lutter

docker/Dockerfile

@@ -58,7 +58,7 @@ EXPOSE 8001
 EXPOSE 8020
 
 RUN apt-get update \
- && apt-get install -y libpq-dev ca-certificates
+ && apt-get install -y libpq-dev ca-certificates netcat
 
 ADD docker/wait_for docker/start /usr/local/bin/
 COPY --from=graph-node-build /usr/local/cargo/bin/graph-node /usr/local/bin