update to latest s6 and alpine

Author: egeland

Dockerfile

@@ -1,5 +1,5 @@
 ARG BASE_IMAGE
-FROM ${BASE_IMAGE:-library/alpine}:3.7
+FROM ${BASE_IMAGE:-library/alpine}:3.8
 
 ARG QEMU_ARCH
 ENV QEMU_ARCH=${QEMU_ARCH:-x86_64} S6_KEEP_ENV=1
@@ -13,7 +13,7 @@ RUN set -x && apk add --no-cache curl coreutils tzdata shadow \
     aarch64) S6_ARCH='aarch64';; \
     *) echo "unsupported architecture"; exit 1 ;; \
   esac \
-  && curl -L -s https://github.com/just-containers/s6-overlay/releases/download/v1.21.1.1/s6-overlay-${S6_ARCH}.tar.gz | tar xvzf - -C / \
+  && curl -L -s https://github.com/just-containers/s6-overlay/releases/download/v1.21.7.0/s6-overlay-${S6_ARCH}.tar.gz | tar xvzf - -C / \
   && groupmod -g 911 users && \
   useradd -u 911 -U -d /config -s /bin/false abc && \
   usermod -G users abc && \