Fix ubuntu version though it shouldnt matter in the future

Dockerfile

@@ -1,9 +1,9 @@
-FROM ubuntu:20.04 as builder
+FROM ubuntu:18.04 as builder
 RUN apt -y update || true; apt -y install gcc
 COPY ./pause /pause
 RUN cd /pause && gcc ./main.c -o pauser
 
-FROM ubuntu:20.04
+FROM ubuntu:18.04
 RUN groupadd postgres && useradd -d /home/postgres -ms /bin/bash -g postgres -G sudo postgres
 RUN export DEBIAN_FRONTEND=noninteractive; \
    apt -y update || true;  \