Updating Python AdX Buyer REST Samples to v1.3

Reviewed in https://codereview.appspot.com/13568043/.
diff --git a/samples/adexchangebuyer/submit_creative.py b/samples/adexchangebuyer/submit_creative.py
index e7ba2d7..e968093 100644
--- a/samples/adexchangebuyer/submit_creative.py
+++ b/samples/adexchangebuyer/submit_creative.py
@@ -43,7 +43,7 @@
 def main(argv):
   # Authenticate and construct service.
   service, flags = sample_tools.init(
-      argv, 'adexchangebuyer', 'v1.2', __doc__, __file__, parents=[argparser],
+      argv, 'adexchangebuyer', 'v1.3', __doc__, __file__, parents=[argparser],
       scope='https://www.googleapis.com/auth/adexchange.buyer')
 
   account_id = flags.account_id