fix notifications scrolling the main column

src/components/post_status_form/post_status_form.js

@@ -486,7 +486,7 @@ const PostStatusForm = {
       const bottomBottomPaddingStr = window.getComputedStyle(bottomRef)['padding-bottom']
       const bottomBottomPadding = pxStringToNumber(bottomBottomPaddingStr)
 
-      const scrollerRef = this.$el.closest('.sidebar-scroller') ||
+      const scrollerRef = this.$el.closest('.column.-scrollable') ||
             this.$el.closest('.post-form-modal-view') ||
             window