simpler sidebar width setting

lms/static/coffee/src/discussion/views/discussion_thread_list_view.coffee

@@ -35,7 +35,8 @@ class @DiscussionThreadListView extends Backbone.View
       sidebar.removeClass('fixed');
       sidebar.css('top', '0');
 
-    sidebarWidth = .32 * $(".discussion-body").width() - 10;
+    # sidebarWidth = .32 * $(".discussion-body").width() - 10;
+    sidebarWidth = .31 * $(".discussion-body").width();
     sidebar.css('width', sidebarWidth + 'px');
 
     sidebarHeight = windowHeight - Math.max(discussionsBodyTop - scrollTop, @sidebar_padding)

lms/static/sass/_discussion.scss

@@ -551,7 +551,7 @@ body.discussion {
   .sidebar {
     float: left;
     @include box-sizing(border-box);
-    width: 32%;
+    width: 31%;
     height: 550px;
     border: 1px solid #aaa;
     box-shadow: 0 1px 2px rgba(0, 0, 0, .05);