upgrade alpine v3.11->3.12.1, dovecot v2.3.9.3->2.3.11.3, socat v1.7.3.3->1.7.3.4

https://github.com/dovecot/core/releases/tag/2.3.10
https://github.com/dovecot/core/releases/tag/2.3.10.1
https://github.com/dovecot/core/releases/tag/2.3.11.3
http://www.dest-unreach.org/socat/doc/CHANGES

Dockerfile

@@ -1,7 +1,7 @@
-FROM alpine:3.11
+FROM alpine:3.12.1
 
-ARG DOVECOT_PACKAGE_VERSION=2.3.9.3-r0
-ARG SOCAT_PACKAGE_VERSION=1.7.3.3-r1
+ARG DOVECOT_PACKAGE_VERSION=2.3.11.3-r1
+ARG SOCAT_PACKAGE_VERSION=1.7.3.4-r0
 RUN apk add --no-cache \
         dovecot-lmtpd=$DOVECOT_PACKAGE_VERSION \
         dovecot-pigeonhole-plugin=$DOVECOT_PACKAGE_VERSION \