Add database migrate for viewer tracking

src/db/4.ts

@@ -0,0 +1,8 @@
+import * as db from "../database";
+
+async function run () {
+	await db.query('ALTER TABLE user_meta ADD viewers int UNSIGNED DEFAULT 0 AFTER live');
+	await db.query('INSERT INTO db_meta (version) VALUES (4)');
+}
+
+export { run }