fix(dependencies): apk-tools upgrade to fix CVE-2021-36159 (#73)

alpine/Dockerfile

@@ -4,14 +4,15 @@ LABEL maintainer="Lukas Holota <[email protected]>"
 
 ENV S6_VERSION="v1.22.1.0"
 ENV CPU_ARCH="amd64"
-
 ENV PUID=7077
 ENV PGID=7077
 ENV S6_BEHAVIOUR_IF_STAGE2_FAILS=2
 
 ADD https://github.com/just-containers/s6-overlay/releases/download/${S6_VERSION}/s6-overlay-${CPU_ARCH}.tar.gz /tmp/
 
 RUN tar xzf /tmp/s6-overlay-${CPU_ARCH}.tar.gz -C / && \
+ # This package is included in the base image. It's explicitly upgrade to avoid CVE-2021-36159
+ apk add --no-cache apk-tools=2.12.7-r0 && \
  apk add --no-cache shadow=4.8.1-r0 && \
  rm /tmp/s6-overlay-${CPU_ARCH}.tar.gz