Use hash stream instead of crypto.createHash

crypto.createHash is a write stream but not a PassThrough stream!

src/backupformat/tgz.js

@@ -8,6 +8,7 @@ const assert = require('assert'),
     debug = require('debug')('box:backupformat/tgz'),
     { DecryptStream, EncryptStream } = require('../hush.js'),
     fs = require('fs'),
+    HashStream = require('../hash-stream.js'),
     path = require('path'),
     ProgressStream = require('../progress-stream.js'),
     promiseRetry = require('../promise-retry.js'),
@@ -141,7 +142,7 @@ async function tarPack(dataLayout, encryption, uploader, progressCallback) {
 
     const pack = tar.pack();
 
-    const hash = crypto.createHash('sha256');
+    const hash = new HashStream();
 
     let pipeline = null;
     if (encryption) {