Ensure live region is appended to role="dialog" (#12)

Fixes: #13

It'd be nice to add tests for dialog scenarios we use ariaNotify in
covering `<dialog>` and `[role="dialog"]`. It doesn't look like there
are any right now - it looks a bit involved, so I will not tackle that
in this PR. Filed:
#14

Author: smockle

ariaNotify-polyfill.js

@@ -73,7 +73,7 @@ if (!("ariaNotify" in Element.prototype)) {
 
       // Get root element
       let root = /** @type {Element} */ (
-        this.element.closest("dialog") || this.element.getRootNode()
+        this.element.closest("dialog") || this.element.closest("[role='dialog']") || this.element.getRootNode()
       );
       if (!root || root instanceof Document) root = document.body;