Update Wall of Browser Bugs entry for #14972

http://crbug.com/175502 is fixed in Chrome 40 and has been closed.
But Windows is still broken due to http://crbug.com/438064 ,
  which is open and currently targeting Chrome 41.
Whitelist <li role="separator">...</li>

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

[skip sauce]
Merge pull request #15269 from twbs/role-separator

Whitelist <li role="separator">...</li>
[skip sauce]
automatic grunt dist
Add keyboard support to dropdown.js
Update component includes with proper dropdown aria/ markup
Update js includes with proper dropdown aria/ markup
Update examples  with proper dropdown aria/ markup
Fix travis HTML errors. Update js based on review