fixed a tiny bug that loading icon sometimes doesn't appear at the right place / doesn't go away

lms/static/coffee/src/discussion/content.coffee

@@ -124,7 +124,7 @@ if Backbone?
         url = @model.urlFor('retrieve')
         DiscussionUtil.safeAjax
           $elem: $elem
-          $loading: $(event.target) if event
+          $loading: @$(".discussion-show-comments")
           type: "GET"
           url: url
           success: (response, textStatus) =>

lms/static/coffee/src/discussion/utils.coffee

@@ -1,9 +1,10 @@
 $ ->
   $.fn.extend
     loading: ->
-      $(this).after("<span class='discussion-loading'></span>")
+      @$_loading = $("<span class='discussion-loading'></span>")
+      $(this).after(@$_loading)
     loaded: ->
-      $(this).parent().children(".discussion-loading").remove()
+      @$_loading.remove()
 
 class @DiscussionUtil