rexml: upgrade to 3.1.8

See https://github.com/ruby/rexml/blob/master/NEWS.md for change summary.

Changes for spec/ has been reported: https://github.com/ruby/spec/pull/639


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66458 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/rexml/parse/test_processing_instruction.rb

@@ -0,0 +1,25 @@
+require "test/unit"
+require "rexml/document"
+
+module REXMLTests
+  class TestParseProcessinInstruction < Test::Unit::TestCase
+    def parse(xml)
+      REXML::Document.new(xml)
+    end
+
+    class TestInvalid < self
+      def test_no_name
+        exception = assert_raise(REXML::ParseException) do
+          parse("<??>")
+        end
+        assert_equal(<<-DETAIL.chomp, exception.to_s)
+Invalid processing instruction node
+Line: 1
+Position: 4
+Last 80 unconsumed characters:
+<??>
+        DETAIL
+      end
+    end
+  end
+end