Pass proper 'this' context to updateSidebar method so that sidebar could resize…

Pass proper 'this' context to updateSidebar method so that sidebar could resize properly on load, scroll.

lms/djangoapps/discussion/static/discussion/js/views/discussion_board_view.js

@@ -53,7 +53,7 @@
                     el: this.$('.forum-search')
                 }).render();
                 this.renderBreadcrumbs();
-                $(window).bind('load scroll resize', this.updateSidebar);
+                $(window).bind('load scroll resize', _.bind(this.updateSidebar, this));
                 this.showBrowseMenu(true);
                 return this;
             },