Incompatible with Ruby >= 2.6 with recent Webrick version

[nbulaj]

Hi! There is an issue with Ruby >= 2.6 with a recent Webrick version. Webrick public API was changed and now it requires more arguments.

Check the do_PUT / do_DELETE / do_PATCH / etc methods that calls perform_proxy_request(req, res) under the hood. But in a new Webrick it requires 3..4 arguments to be passed:

https://github.com/ruby/webrick/blob/master/lib/webrick/httpproxy.rb#L298

So we catch wrong number of arguments (given 2, expected 3..4) exception.

[drbig]

Indeed. Perhaps easiest is to RVM an older version... not that this approach has been proven sane (looking at some Pythons...).