5.1.1: Plugin installation behind Proxy

Can I have a definitive statement on the fix for this please? I've upgraded to 5.2.0 and i still cannot install plugins. And, the above workaround fails too:

# bin/logstash-plugin install logstash-filter-de_dot
Validating logstash-filter-de_dot
Installing logstash-filter-de_dot
Error Bundler::InstallError, retrying 1/10
An error occurred while installing logstash-core-event-java (5.2.0), and Bundler cannot continue.
Make sure that `gem install logstash-core-event-java -v '5.2.0'` succeeds before bundling.
WARNING: SSLSocket#session= is not supported

Regards,
David