use buster for image instead of stable as debian released a new version

Author: jc21

docker/Dockerfile

@@ -2,7 +2,7 @@
 # Certbot Builder
 #############
 
-FROM debian:stable-slim as certbotbuilder
+FROM debian:buster-slim as certbotbuilder
 
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 
@@ -43,7 +43,7 @@ RUN pip install --no-cache-dir cffi certbot
 # Nginx Builder
 #############
 
-FROM debian:stable-slim as nginxbuilder
+FROM debian:buster-slim as nginxbuilder
 
 ARG OPENRESTY_VERSION
 ARG LUA_VERSION
@@ -73,13 +73,13 @@ RUN /tmp/build-openresty
 # Final Image
 #############
 
-FROM debian:stable-slim
+FROM debian:buster-slim
 LABEL maintainer="Jamie Curnow <[email protected]>"
 
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 
 ARG TARGETPLATFORM
-RUN echo "Base: debian:stable-slim, ${TARGETPLATFORM:-linux/amd64}" > /built-for-arch
+RUN echo "Base: debian:buster-slim, ${TARGETPLATFORM:-linux/amd64}" > /built-for-arch
 
 # OpenResty uses LuaJIT which has a dependency on GCC
 RUN apt-get update \