🔧 add files field

Author: 59naga

package.json

@@ -2,6 +2,7 @@
   "name": "socket.io-middleware-firebase-admin",
   "version": "0.0.1",
   "description": "a socket.io middleware firebaseAdmin.verifySessionCookie",
+  "files": ["index.js", "index.mjs"],
   "scripts": {
     "start": "abby format, test --watch \"*.mjs\"",
     "test": "node --experimental-modules test.mjs",