Changed Ruby dependency to 2.7.3.

containers/zammad/Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:2.6.6-slim AS builder
+FROM ruby:2.7.3-slim AS builder
 # note: zammad is currently incompatible to alpine because of:
 # https://github.com/docker-library/ruby/issues/113
 
@@ -24,7 +24,7 @@ RUN chmod +x /tmp/setup.sh; \
     /tmp/setup.sh builder
 
 
-FROM ruby:2.6.6-slim
+FROM ruby:2.7.3-slim
 
 ARG BUILD_DATE
 ARG DEBIAN_FRONTEND=noninteractive