Fix expected extension for CIPD on Windows

New depot_tools copy is a batch file

BUG=skia:

Change-Id: Id1497f7f7d7d93600fbfbf5991f7582380781ae8
Reviewed-on: https://skia-review.googlesource.com/9896
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

infra/bots/assets/asset_utils.py

@@ -49,7 +49,7 @@ class CIPDStore(object):
   def __init__(self, cipd_url=DEFAULT_CIPD_SERVICE_URL):
     self._cipd = 'cipd'
     if sys.platform == 'win32':
-      self._cipd = 'cipd.exe'
+      self._cipd = 'cipd.bat'
     self._cipd_url = cipd_url
     self._check_setup()