Add missing require

src/cron.js

@@ -33,9 +33,10 @@ var appHealthMonitor = require('./apphealthmonitor.js'),
     settings = require('./settings.js'),
     system = require('./system.js'),
     updater = require('./updater.js'),
-    updateChecker = require('./updatechecker.js');
+    updateChecker = require('./updatechecker.js'),
+    _ = require('underscore');
 
-var gJobs = {
+const gJobs = {
     autoUpdater: null,
     backup: null,
     updateChecker: null,
@@ -51,7 +52,7 @@ var gJobs = {
     appHealthMonitor: null
 };
 
-var NOOP_CALLBACK = function (error) { if (error) debug(error); };
+const NOOP_CALLBACK = function (error) { if (error) debug(error); };
 
 // cron format
 // Seconds: 0-59