hpricot：Hpricot::Builder#doctype

everyday Ruby 
>> require "hpricot"
=> true
>> doc = Hpricot('') {}
=> #<Hpricot::Doc>
>> doc.doctype('HTML', 'hoge')
ArgumentError: wrong number of arguments (2 for 3)
	from (irb):3:in `doctype'
	from (irb):3
>> doc.doctype('HTML', 'hoge', '')
/usr/local/ruby-1.8.7/lib/ruby/gems/1.8/gems/hpricot-0.8.2/lib/hpricot/tag.rb:181: [BUG] Segmentation fault
ruby 1.8.7 (2010-01-10 patchlevel 249) [i686-linux]