Update presubmit branch check text for git 1.8

PRESUBMIT.py

 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Documentation on PRESUBMIT.py can be found at:
 # http://www.chromium.org/developers/how-tos/depottools/presubmit-scripts
 
 EXCLUDE_PROJECT_CHECKS_DIRS = [ '.' ]
 
 import subprocess
 def CheckGitBranch():
   p = subprocess.Popen("git branch -vv", shell=True,
                        stdout=subprocess.PIPE)
   output, _ = p.communicate()
 
   lines = output.split('\n')
   for line in lines:
     # output format for checked-out branch should be
     # * branchname hash [TrackedBranchName ...
     toks = line.split()
     if '*' not in toks[0]:
       continue
     if not 'origin/master' in toks[3]:
       warning = 'Warning: your current branch:\n' + line
       warning += '\nis not tracking origin/master. git cl push may silently '
       warning += 'fail to push your change. To fix this, do\n'
-      warning += 'git branch --set-upstream '+ toks[1] + ' origin/master'
+      warning += 'git branch -u origin/master'
       return warning
     return None
   print 'Warning: presubmit check could not determine local git branch'
   return None
 
 def _CommonChecks(input_api, output_api):
   """Checks for both upload and commit."""
   results = []
   results.extend(input_api.canned_checks.PanProjectChecks(
       input_api, output_api, project_name='Native Client',
@@ skipping 19 matching lines @@
   Args:
     input_api: the limited set of input modules allowed in presubmit.
     output_api: the limited set of output modules allowed in presubmit.
   """
   report = []
   report.extend(CheckChangeOnUpload(input_api, output_api))
   return report
 
 def GetPreferredTrySlaves(project, change):
   return []