Temporarily allow jruby-head failures on CI
Temporarily allow jruby-head failures on CI

There's a pull request pending to fix JRuby's deprecation messages,
however some specs there fail, and there's no certainty when it will be
merged.
https://github.com/jruby/jruby/pull/6166

rspec/rspec-rails,rspec/rspec-rails,rspec/rspec-rails