Mark spec as ruby_bug until 2.5.1 is released
Mark spec as ruby_bug until 2.5.1 is released

* To pass all specs with the latest 2.5 release.

ruby/spec,nobu/rubyspec,nobu/rubyspec,eregon/rubyspec,ruby/spec,ruby/rubyspec,eregon/rubyspec,ruby/rubyspec,eregon/rubyspec,ruby/spec,nobu/rubyspec