Whitelist <li role="separator">...</li>

Refs https://www.w3.org/Bugs/Public/show_bug.cgi?id=27120
Refs #15263

[skip sauce]

Gruntfile.js

@@ -331,7 +331,8 @@ module.exports = function (grunt) {
         relaxerror: [
           'Element img is missing required attribute src.',
           'Attribute autocomplete not allowed on element input at this point.',
-          'Attribute autocomplete not allowed on element button at this point.'
+          'Attribute autocomplete not allowed on element button at this point.',
+          'Bad value separator for attribute role on element li.'
         ]
       },
       files: {