chore: specific tsdown target

Author: 9romise

tsdown.config.ts

@@ -1,6 +1,7 @@
 import { defineConfig } from 'tsdown'
 
 export default defineConfig({
+  target: 'node18',
   entry: ['lib/index.js'],
   format: ['cjs'],
   copy: ['lib/index.d.ts'],