Fix EventTile typing

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

src/components/views/rooms/EventTile.tsx

@@ -320,7 +320,7 @@ export default class EventTile extends React.Component<IProps, IState> {
     private suppressReadReceiptAnimation: boolean;
     private isListeningForReceipts: boolean;
     private tile = React.createRef();
-    private replyThread = React.createRef();
+    private replyThread = React.createRef<ReplyThread>();
 
     public readonly ref = createRef<HTMLElement>();