logstash: re-add bundle update and update bundler (#5284)

* update to latest logstash and bundler

Signed-off-by: Edward Welch <edward.welch@grafana.com>

* re-add bundle update

Signed-off-by: Edward Welch <edward.welch@grafana.com>

clients/cmd/logstash/Dockerfile

@@ -1,4 +1,4 @@
-FROM logstash:7.16.1
+FROM logstash:7.16.3
 
 USER logstash
 ENV PATH /usr/share/logstash/vendor/jruby/bin:/usr/share/logstash/vendor/bundle/jruby/2.5.0/bin:/usr/share/logstash/jdk/bin:$PATH
@@ -6,13 +6,14 @@ ENV LOGSTASH_PATH /usr/share/logstash
 ENV GEM_PATH /usr/share/logstash/vendor/bundle/jruby/2.5.0
 ENV GEM_HOME /usr/share/logstash/vendor/bundle/jruby/2.5.0
 
-RUN gem install bundler:2.1.4
+RUN gem install bundler:2.3.6
 
 COPY --chown=logstash:logstash ./clients/cmd/logstash/ /home/logstash/
 WORKDIR /home/logstash/
 
 RUN bundle config set --local path /usr/share/logstash/vendor/bundle && \
     bundle install && \
+    bundle update && \
     bundle exec rake vendor && \
     bundle exec rspec