Fix an assignment bug in jruby 9.0.0.0.
Fix an assignment bug in jruby 9.0.0.0.

Getting failures like:

  1) Honeybadger::Notice exception cause when raising CauseError with a
cause stops unwrapping at 5
     Failure/Error: expect(causes.size).to eq 5

       expected: 5
            got: 0

       (compared using ==)
     # ./spec/unit/honeybadger/notice_spec.rb:740:in `(root)'

Workable/honeybadger-ruby,gtd/honeybadger-ruby,gtd/honeybadger-ruby,kylerippey/honeybadger-ruby,honeybadger-io/honeybadger-ruby,Workable/honeybadger-ruby,kylerippey/honeybadger-ruby,honeybadger-io/honeybadger-ruby