Fix failing tests with rexml 3.4.2

[dalibor]

Fixes #43

With REXML 3.4.2, REXML::Document.new raises an error if a <!DOCTYPE> declaration is present but no root element has been defined.

rexml-3.4.2/lib/rexml/source.rb:275:in 'REXML::IOSource#read_until': undefined method 'eof?' for nil (NoMethodError)

        read if @scanner.eos? and [email protected]?

[jessebs]

Thank you for the quick fix!

[kou]

This is a correct fix (as a REXML maintainer view).

In this case, REXML::Document.new raises a non-expected error but REXML::Document.new must reject invalid XML. In this case, no root element XML is an invalid XML.

[btihen]

Cool - thanks!