Issue 4795 - Use modern JavaScript syntax

lib/io.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 35 matching lines @@
     {
       content: Array.from(data),
       lastModified: Date.now()
     },
     callback
   );
 }
 
 exports.IO =
 {
-  resolveFilePath: path => new FakeFile(path),
+  resolveFilePath(path) { return new FakeFile(path); },
 
-  readFromFile: (file, listener, callback) =>
+  readFromFile(file, listener, callback)
   {
     function onLoaded(entry)
     {
       for (let line of entry.content)
         listener.process(line);
 
       listener.process(null);
       callback(null);
     }
 
     loadFile(file, onLoaded, callback);
   },
 
-  writeToFile: (file, data, callback) =>
+  writeToFile(file, data, callback)
   {
     saveFile(file, data, callback);
   },
 
-  copyFile: (fromFile, toFile, callback) =>
+  copyFile(fromFile, toFile, callback)
   {
     function onLoaded(entry)
     {
       saveFile(toFile, entry.content, callback);
     }
 
     loadFile(fromFile, onLoaded, callback);
   },
 
-  renameFile: (fromFile, newName, callback) =>
+  renameFile(fromFile, newName, callback)
   {
     function onLoaded(entry)
     {
       ext.storage.remove(fileToKey(fromFile), () =>
       {
         ext.storage.set(keyPrefix + newName, entry, callback);
       });
     }
 
     loadFile(fromFile, onLoaded, callback);
   },
 
-  removeFile: (file, callback) =>
+  removeFile(file, callback)
   {
     ext.storage.remove(fileToKey(file), callback);
   },
 
-  statFile: (file, callback) =>
+  statFile(file, callback)
   {
     function onLoaded(entry)
     {
       callback(null, {
         exists: true,
         lastModified: entry.lastModified
       });
     }
 
     loadFile(file, onLoaded, callback);
   }
 };