S3Adapter: expose the object and use => for s3.upload callback

S3Adapter.js

@@ -40,7 +40,7 @@ S3Adapter.prototype.create = function(config, filename, data) {
   }
 
   return new Promise((resolve, reject) => {
-    this.s3.upload(params, function(err, data) {
+    this.s3.upload(params, (err, data) => {
       if (err !== null) return reject(err);
       resolve(data);
     });

index.js

@@ -6,6 +6,7 @@ var batch = require('./batch'),
     DatabaseAdapter = require('./DatabaseAdapter'),
     express = require('express'),
     FilesAdapter = require('./FilesAdapter'),
+    S3Adapter = require('./S3Adapter'),
     middlewares = require('./middlewares'),
     multer = require('multer'),
     Parse = require('parse/node').Parse,
@@ -179,5 +180,6 @@ function getClassName(parseClass) {
 }
 
 module.exports = {
-  ParseServer: ParseServer
+  ParseServer: ParseServer,
+  S3Adapter: S3Adapter
 };