Update Dockerfile.prod

Author: naraesk

evaluationserver/Dockerfile.prod

@@ -6,7 +6,7 @@ RUN apt-get update \
 RUN mkdir -p /usr/src/app
 WORkDIR /usr/src/app/
 COPY . .
-RUN gem install bundler && bundle install --jobs 20 --retry 5 # might be better?
+RUN gem install bundler && bundle binstub bundler --force && bundle install --jobs 20 --retry 5 # might be better?
 RUN gem install bundler
 ENV RAILS_ENV production
 RUN bundle binstub bundler --force