Fix drop index

src/models/stats.ts

@@ -2,7 +2,12 @@ import * as mongo from 'mongodb';
 import db from '../db/mongodb';
 
 const Stats = db.get<IStats>('stats');
-Stats.dropIndex({ date: -1 } as any); // 後方互換性のため
+
+// 後方互換性のため
+Stats.dropIndex({ date: -1 } as any).catch((e: mongo.MongoError) => {
+	if (e.code !== 27) throw e;
+});
+
 Stats.createIndex({ span: -1, date: -1 }, { unique: true });
 export default Stats;