use cjs to transpile the mjs

package.json

@@ -13,7 +13,7 @@
     "build": "npm run prepare",
     "pretest": "npm run prepare",
     "presnap": "npm run prepare",
-    "prepare": "node ./scripts/transpile-to-esm.mjs",
+    "prepare": "node ./scripts/transpile-to-esm.js",
     "size": "size-limit",
     "test": "tap",
     "snap": "tap",

scripts/transpile-to-esm.js

@@ -0,0 +1,7 @@
+#!/usr/bin/env node
+
+const { readFileSync, writeFileSync } = require('fs')
+const { resolve } = require('path')
+const cjs = readFileSync(resolve(__dirname, '../index.js'), 'utf8')
+const esm = cjs.replace(/module.exports\s*=\s*/, 'export default ')
+writeFileSync(resolve(__dirname, '../index.mjs'), esm, 'utf8')