Issue 427 - Remove non-standard function and getter syntax

lib/synchronizer.js

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2014 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 293 matching lines @@
             return;
 
           if (!(subscription.url in FilterStorage.knownSubscriptions))
             return;
 
           let match = /^(\d+)(?:\s+(\S+))?$/.exec(request.responseText);
           if (match && match[1] == "301" && match[2] && /^https?:\/\//i.test(match[2])) // Moved permanently
             redirectCallback(match[2]);
           else if (match && match[1] == "410")        // Gone
           {
-            let data = "[Adblock]\n" + subscription.filters.map(function(f) f.text).join("\n");
+            let data = "[Adblock]\n" + subscription.filters.map((f) => f.text).join("\n");
             redirectCallback("data:text/plain," + encodeURIComponent(data));
           }
         }, false);
         request.send(null);
       }
     }
   },
 };
 Synchronizer.init();