Update datastore doctests to reflect change in cursor behavior. (#4382)
Update datastore doctests to reflect change in cursor behavior. (#4382)

Follow up to #4349.
jonparrott/google-cloud-python,tseaver/google-cloud-python,tswast/google-cloud-python,tswast/google-cloud-python,dhermes/google-cloud-python,dhermes/google-cloud-python,tswast/google-cloud-python,GoogleCloudPlatform/gcloud-python,dhermes/google-cloud-python,tseaver/google-cloud-python,tseaver/google-cloud-python,dhermes/gcloud-python,googleapis/google-cloud-python,jonparrott/google-cloud-python,dhermes/gcloud-python,tseaver/gcloud-python,tseaver/gcloud-python,jonparrott/gcloud-python,GoogleCloudPlatform/gcloud-python,jonparrott/gcloud-python,googleapis/google-cloud-python