Cleanup pylint errors

test/msvs/buildevents/gyptest-ninja-warnings.py

 #!/usr/bin/env python
 
 # Copyright (c) 2014 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Verifies that ninja errors out when encountering msvs_prebuild/msvs_postbuild.
 """
 
 import sys
 import TestCmd
 import TestGyp
 
 
 if sys.platform == 'win32':
   test = TestGyp.TestGyp(formats=['ninja'])
 
   test.run_gyp('buildevents.gyp',
       status=1,
-      stderr='.*msvs_prebuild not supported \(target main\).*',
+      stderr=r'.*msvs_prebuild not supported \(target main\).*',
       match=TestCmd.match_re_dotall)
 
   test.run_gyp('buildevents.gyp',
       status=1,
-      stderr='.*msvs_postbuild not supported \(target main\).*',
+      stderr=r'.*msvs_postbuild not supported \(target main\).*',
       match=TestCmd.match_re_dotall)
 
   test.pass_test()