Fix incorrect function being used

src/webui/www/private/newcategory.html

@@ -89,7 +89,7 @@
                                     }
                                 }).send();
                             },
-                            onError: function() {
+                            onFailure: function() {
                                 alert("QBT_TR(Unable to create category)QBT_TR[CONTEXT=HttpServer] " + window.qBittorrent.Misc.escapeHtml(categoryName));
                             }
                         }).send();