root/pypi: links for proto-google-cloud-spanner-admin-instance-v1

root/pypi proto-google-cloud-spanner-admin-instance-v1-0.15.3.tar.gz
root/pypi proto-google-cloud-spanner-admin-instance-v1-0.15.1.tar.gz
root/pypi proto-google-cloud-spanner-admin-instance-v1-0.15.0.tar.gz