[ruby/rdoc] Convert tick double quote in character entity references

https://github.com/ruby/rdoc/commit/6ed889aac9

lib/rdoc/text.rb

@@ -237,7 +237,7 @@ module RDoc::Text
       when s.scan(/``/) then # backtick double quote
         html << encoded[:open_dquote]
         after_word = nil
-      when s.scan(/''/) then # tick double quote
+      when s.scan(/(?:&#39;|'){2}/) then # tick double quote
         html << encoded[:close_dquote]
         after_word = nil
       when s.scan(/`/) then # backtick

test/rdoc/test_rdoc_text.rb

@@ -514,6 +514,7 @@ The comments associated with
   def test_to_html_double_backtick
     assert_equal '“a',  to_html('``a')
     assert_equal '“a“', to_html('``a``')
+    assert_equal '“a”', to_html("``a''")
   end
 
   def test_to_html_double_quote