Fix typo on test/test_sax_parser.rb
Fix typo on test/test_sax_parser.rb

s/refuse_nil/refute_nil/

Signed-off-by: Sergio Durigan Junior <b228c7af5dad25c96a60cf772bbe0766d05c067e@canonical.com>

xml4r/libxml-ruby,xml4r/libxml-ruby,xml4r/libxml-ruby