fix(Dropdown): accessibility problem (screen readers) (#1836)

* fix(Dropdown): accessibility problem (screen readers)(#1834)

*  fix(Dropdown): accessibility problem (screen readers)(#1834)
		- Dropdown.js --> coded added now is more simple.

* fix(Dropdown): accessibility problem (screen readers)(#1834)
	- patched an error. Forgotten '}'

* fix(Dropdown): accessibility problem (screen readers)(#1834)
        - Dropdown.js->renderTex--> now always returns the text rendered with aria labels: role='alert' aria-live='polite'

* fix lint issue

src/modules/Dropdown/Dropdown.js

@@ -1094,7 +1094,7 @@ export default class Dropdown extends Component {
       _text = _.get(this.getItemByValue(value), 'text')
     }
 
-    return <div className={classes}>{_text}</div>
+    return <div className={classes} role='alert' aria-live='polite'>{_text}</div>
   }
 
   renderSearchInput = () => {