swap redis client gem in used in docker image

Author: porbas

contrib/ruby_event_store-outbox/Dockerfile

@@ -2,5 +2,5 @@ FROM ruby:2.7
   ARG GEM_VERSION
   RUN gem install ruby_event_store-outbox --version $GEM_VERSION
   RUN gem install influxdb --version 0.8.1
-  RUN gem install redis mysql2
+  RUN gem install redis-client mysql2
   ENTRYPOINT ["/usr/local/bundle/bin/res_outbox"]