Update datastore batch API doc reference.

Author: daspecster

packages/google-cloud-datastore/google/cloud/datastore/batch.py

@@ -18,7 +18,7 @@
 in a single request to the Cloud Datastore API.
 
 See
-https://cloud.google.com/datastore/docs/concepts/entities#Datastore_Batch_operations
+https://cloud.google.com/datastore/docs/concepts/entities#batch_operations
 """
 
 from google.cloud.datastore import helpers