use transaction for migration

go/migrations/000013_network_billing.down.sql

@@ -1,2 +1,6 @@
+BEGIN;
+
 DROP TABLE IF EXISTS network_subscriptions;
 DROP TABLE IF EXISTS network_stripe_customers;
+
+COMMIT;

go/migrations/000013_network_billing.up.sql

@@ -1,3 +1,5 @@
+BEGIN;
+
 CREATE TABLE network_stripe_customers (
   network_id         TEXT PRIMARY KEY,
   stripe_customer_id TEXT NOT NULL UNIQUE,
@@ -22,3 +24,5 @@ CREATE TABLE network_subscriptions (
 
 CREATE UNIQUE INDEX idx_network_subscriptions_network_id
   ON network_subscriptions (network_id);
+
+COMMIT;