feat(tabs): verify click tabNode using *[role=tab] (#220)

Implementing `react-tabs` with a custom `TabList` & `Tab` components can be currently done by using the corresponding `tabRole` static in custom components. This is neat. However, the check within `isTabNode()` relies on the tagName being an `LI` element, and this has some limitations for cases where the `tabList` markup isn't done using a `ul > li` structure.

src/components/UncontrolledTabs.js

@@ -9,7 +9,7 @@ import { isTabList, isTabPanel, isTab } from '../helpers/elementTypes';
 
 // Determine if a node from event.target is a Tab element
 function isTabNode(node) {
-  return node.nodeName === 'LI' && node.getAttribute('role') === 'tab';
+  return node.getAttribute('role') === 'tab';
 }
 
 // Determine if a tab node is disabled