Silence usages of componentWillReceiveProps

For https://github.com/vector-im/riot-web/issues/12877

src/components/views/elements/Dropdown.js

@@ -128,7 +128,8 @@ export default class Dropdown extends React.Component {
         document.removeEventListener('click', this._onDocumentClick, false);
     }
 
-    componentWillReceiveProps(nextProps) {
+    // TODO: [REACT-WARNING] Replace with appropriate lifecycle event
+    UNSAFE_componentWillReceiveProps(nextProps) {
         if (!nextProps.children || nextProps.children.length === 0) {
             return;
         }