wrong content in jruby when node includes new lines

[esse]

Steps to reproduce:

1. write string containing new line inside it, for example:

</div>```


2. parse it using nokogiri for ruby - html.content will return \n as expected

3. parse it using nokogiri for jruby - html.content will return empty string - as unexpected


This test case is inside test/html/test_document.rb file (test: test_content_size).

Second commit contain fix for this bug (inside XmlNode.java).