Fix test in a cross-ruby way

Author: drbrain

test/test_rdoc_markup_to_html_snippet.rb

@@ -543,11 +543,12 @@ def test_convert_limit_verbatim_multiline
 This routine modifies its +comment+ parameter.
     RDOC
 
+    inner = CGI.escapeHTML "# Don't display comment from this point forward"
     expected = <<-EXPECTED
 <p>Look for directives in a normal comment block:
 
 <pre># :stopdoc:
-# Don&#39;t display comment from this point forward</pre>
+#{inner}</pre>
     EXPECTED
 
     actual = @to.convert rdoc