make compatible w/ ESM

Author: alexfu

source/util/migration_handler.ts

@@ -1,8 +1,8 @@
-import { Client } from 'pg'
+import pg from 'pg'
 import { migrate } from 'postgres-migrations'
 
 export async function applyMigrations(config: any): Promise<void> {
-	const client = new Client(config)
+	const client = new pg.Client(config)
 	await client.connect()
 	try {
 		await migrate({ client }, __dirname + '/migrations')