change TruffleRuby's RUBY_ENGINE to ruby until we are recognised by rubygems
change TruffleRuby's RUBY_ENGINE to ruby until we are recognised by rubygems

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