Lock Dockerfile to Ruby 2.7

Signed-off-by: Robert Clark <[email protected]>

Author: Robert Clark

Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:alpine as builder
+FROM ruby:2-alpine as builder
 
 LABEL name="Heimdall Tools" \
       vendor="MTIRE" \
@@ -18,13 +18,13 @@ RUN cd /build && \
       gem build heimdall_tools.gemspec -o heimdall_tools.gem
 
 
-FROM ruby:alpine
+FROM ruby:2-alpine
 
 RUN apk add --no-cache build-base
 
 COPY --from=builder /build/heimdall_tools.gem /build/
 RUN gem install build/heimdall_tools.gem
-    
+
 RUN apk del build-base
 
 ENTRYPOINT ["heimdall_tools"]