Correct $window to $(window) in application.js

app/assets/javascripts/application.js.coffee

@@ -255,7 +255,7 @@ $ ->
   new Aside()
 
   # Sidenav pinning
-  if $window.width() < 1280 and $.cookie('pin_nav') is 'true'
+  if $(window).width() < 1280 and $.cookie('pin_nav') is 'true'
     $.cookie('pin_nav', 'false', { path: '/' })
     $('.page-with-sidebar')
       .toggleClass('page-sidebar-collapsed page-sidebar-expanded')