upgrade alpine base image v3.12.3->3.13.0 including openssh-server package upgrade v8.3_p1-r1->v8.4_p1-r2 (diff links below)

https://www.openssh.com/txt/release-8.4

https://git.alpinelinux.org/aports/commit/?id=271a173d27e313f80d3c0a7c0c0e4b9060e55e6d
https://git.alpinelinux.org/aports/commit/?id=be38ca6bc1abd987c47227b7b0025e12c39dcbfa
https://git.alpinelinux.org/aports/commit/?id=ec4425ce83436793a42ac9784b717644fe05479a

Dockerfile

@@ -1,6 +1,6 @@
-FROM alpine:3.12.3
+FROM alpine:3.13.0
 
-ARG OPENSSH_SERVER_PACKAGE_VERSION=8.3_p1-r1
+ARG OPENSSH_SERVER_PACKAGE_VERSION=8.4_p1-r2
 RUN apk add --no-cache openssh-server=$OPENSSH_SERVER_PACKAGE_VERSION
 
 ENV SSHD_HOST_KEYS_DIR /etc/ssh/host_keys