Dockerfile in postfix-exporter-2.0.2 vs Dockerfile in postfix-exporter-2.0.3

@@ -1,9 +1,11 @@
 FROM ruby:2.3-alpine
 
+ARG GEM_VERSION="> 0"
+
 RUN apk update \
 	&& apk add build-base \
-	&& gem install postfix-exporter \
+	&& gem install postfix-exporter -v "$GEM_VERSION" \
 	&& apk del build-base \
 	&& rm -f /var/cache/apk/*
 
 ENTRYPOINT ["/usr/local/bundle/bin/postfix-exporter"]