Fixes transactional_retry region tag

Author: WalterHub

datastore/api/snippets.py

@@ -663,7 +663,7 @@ def transfer_funds(client, from_key, to_key, amount):
             transfer_funds(client, account1.key, account2.key, 50)
         except gcloud.exceptions.Conflict:
             continue
-    # [END transaction_retry]
+    # [END transactional_retry]
 
     return account1.key, account2.key