Change default gsutil.py version to 4.13

gsutil.py

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Run a pinned gsutil."""
 
 
 import argparse
 import base64
@@ skipping 90 matching lines @@
   if force_version:
     gsutil_bin = ensure_gsutil(force_version, target)
   else:
     gsutil_bin = fallback
   cmd = [sys.executable, gsutil_bin] + args
   return subprocess.call(cmd)
 
 
 def parse_args():
   parser = argparse.ArgumentParser()
-  parser.add_argument('--force-version')
+  parser.add_argument('--force-version', default='4.13')
   parser.add_argument('--fallback', default=DEFAULT_FALLBACK_GSUTIL)
   parser.add_argument('--target', default=DEFAULT_BIN_DIR)
   parser.add_argument('args', nargs=argparse.REMAINDER)
 
   args, extras = parser.parse_known_args()
   if args.args and args.args[0] == '--':
     args.args.pop(0)
   if extras:
     args.args = extras + args.args
   return args.force_version, args.fallback, args.target, args.args
 
 
 def main():
   force_version, fallback, target, args = parse_args()
   return run_gsutil(force_version, fallback, target, args)
 
 if __name__ == '__main__':
   sys.exit(main())