Update 12+ to buster

This is an initial attempt to get ahead of #582 at least for newer PostgreSQL releases.

Author: tianon

Diff for: 12/Dockerfile

@@ -1,5 +1,5 @@
 # vim:set ft=dockerfile:
-FROM debian:stretch-slim
+FROM debian:buster-slim
 
 RUN set -ex; \
 	if ! command -v gpg > /dev/null; then \
@@ -71,7 +71,7 @@ RUN set -ex; \
 	apt-key list
 
 ENV PG_MAJOR 12
-ENV PG_VERSION 12~beta1-1.pgdg90+1
+ENV PG_VERSION 12~beta1-1.pgdg100+1
 
 RUN set -ex; \
 	\
@@ -82,20 +82,20 @@ RUN set -ex; \
 	case "$dpkgArch" in \
 		amd64|i386|ppc64el) \
 # arches officialy built by upstream
-			echo "deb http://apt.postgresql.org/pub/repos/apt/ stretch-pgdg main $PG_MAJOR" > /etc/apt/sources.list.d/pgdg.list; \
+			echo "deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main $PG_MAJOR" > /etc/apt/sources.list.d/pgdg.list; \
 			apt-get update; \
 			;; \
 		*) \
 # we're on an architecture upstream doesn't officially build for
 # let's build binaries from their published source packages
-			echo "deb-src http://apt.postgresql.org/pub/repos/apt/ stretch-pgdg main $PG_MAJOR" > /etc/apt/sources.list.d/pgdg.list; \
+			echo "deb-src http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main $PG_MAJOR" > /etc/apt/sources.list.d/pgdg.list; \
 			\
 			case "$PG_MAJOR" in \
 				9.* | 10 ) ;; \
 				*) \
 # https://github.com/docker-library/postgres/issues/484 (clang-6.0 required, only available in stretch-backports)
 # TODO remove this once we hit buster+
-					echo 'deb http://deb.debian.org/debian stretch-backports main' >> /etc/apt/sources.list.d/pgdg.list; \
+					echo 'deb http://deb.debian.org/debian buster-backports main' >> /etc/apt/sources.list.d/pgdg.list; \
 					;; \
 			esac; \
 			\

Diff for: update.sh

@@ -12,9 +12,14 @@ versions=( "${versions[@]%/}" )
 # sort version numbers with highest last (so it goes first in .travis.yml)
 IFS=$'\n'; versions=( $(echo "${versions[*]}" | sort -V) ); unset IFS
 
-defaultDebianSuite='stretch-slim'
+defaultDebianSuite='buster-slim'
 declare -A debianSuite=(
-	#[9.6]='jessie'
+	# https://github.com/docker-library/postgres/issues/582
+	[9.4]='stretch-slim'
+	[9.5]='stretch-slim'
+	[9.6]='stretch-slim'
+	[10]='stretch-slim'
+	[11]='stretch-slim'
 )
 defaultAlpineVersion='3.9'
 declare -A alpineVersion=(