Add migration script for channel bans table in the database.

src/db/3.ts

@@ -0,0 +1,9 @@
+import * as db from "../database";
+
+async function run () {
+	await db.query('CREATE TABLE IF NOT EXISTS ch_bans(channel VARCHAR(25), target VARCHAR(45), time BIGINT, length INT DEFAULT 30)');
+	await db.query('INSERT INTO ch_bans(channel) SELECT username FROM users');
+	await db.query('INSERT INTO db_meta (version) VALUES (3)');
+}
+
+export { run }