Invalid syntax on database table, example should work against 1.0

Example should work against 1.0

CockroachDB node starting at 2017-09-21 14:26:59.087913381 -0500 CDT
build: CCL v1.0.5 @ 2017/08/24 17:43:46 (go1.8.3)
admin: http://jackburton:2800
sql: postgresql://root@jackburton:26257?sslmode=disable
logs: /home/wdroste/tmp/cockroach-data/logs
store[0]: path=/home/wdroste/tmp/cockroach-data
status: initialized new cluster
clusterID: e21342a8-06c0-41a8-bde8-3c1230ed0d72
nodeID: 1

CREATE TABLE IF NOT EXISTS product_orders (
id SERIAL PRIMARY KEY,
product_id INT REFERENCES products(id),
order_id INT REFERENCES orders(id) ON DELETE CASCADE
);
invalid syntax: statement ignored: unimplemented at or near "cascade"

找到包含 CREATE TABLE 语句的示例，并在 CockroachDB 1.0 上复现该示例。调查报告中指出的尚未实现的 ON DELETE CASCADE 语法，然后验证该示例在所述版本上运行时不会出现 invalid-syntax 错误。

由索引模型根据 Issue 内容生成。