Enable 2.4.0 in CI
Enable 2.4.0 in CI

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