Adding react scrollbar to the RHS thread (#2693)

* Adding scrollbar to the RHS thread

* Fixing the RHS thread scrolling issue

webapp/components/create_comment.jsx

@@ -203,7 +203,7 @@ class CreateComment extends React.Component {
         draft.message = messageText;
         PostStore.storeCommentDraft(this.props.rootId, draft);
 
-        $('.post-right__scroll').scrollTop($('.post-right__scroll')[0].scrollHeight);
+        $('.post-right__scroll').parent().scrollTop($('.post-right__scroll')[0].scrollHeight);
         this.setState({messageText: messageText});
     }
     handleKeyDown(e) {