fix: fix the ES module wrapper

The package does not have a default export, so importing it from a
project using ES modules would break in some cases.

> Cannot destructure property 'Server' of '_engineIo.default'

Related: https://github.com/socketio/engine.io/issues/657

examples/esm-import/README.md

@@ -0,0 +1,6 @@
+## How to use
+
+```
+$ npm link ../..
+$ node index.js
+```

examples/esm-import/index.js

@@ -0,0 +1,3 @@
+import { Server } from "engine.io";
+
+console.log(Server);

examples/esm-import/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "esm-import",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module"
+}

package.json

@@ -62,8 +62,8 @@
     "test:compat-v3": "EIO_CLIENT=3 mocha --exit",
     "test:eiows": "EIO_WS_ENGINE=eiows mocha --exit",
     "test:uws": "EIO_WS_ENGINE=uws mocha --exit",
-    "format:check": "prettier --check \"lib/**/*.ts\" \"test/**/*.js\"",
-    "format:fix": "prettier --write \"lib/**/*.ts\" \"test/**/*.js\"",
+    "format:check": "prettier --check \"wrapper.mjs\" \"lib/**/*.ts\" \"test/**/*.js\"",
+    "format:fix": "prettier --write \"wrapper.mjs\" \"lib/**/*.ts\" \"test/**/*.js\"",
     "prepack": "npm run compile"
   },
   "repository": {

wrapper.mjs

@@ -1,3 +1,10 @@
-import lib from "./build/engine.io.js";
-
-export const { Server, Socket, Transport, transports, listen, attach, parser, protocol } = lib;
+export {
+  Server,
+  Socket,
+  Transport,
+  transports,
+  listen,
+  attach,
+  parser,
+  protocol,
+} from "./build/engine.io.js";