fix: improve compatibility with node16 module resolution (#689)

Related: microsoft/TypeScript#46770 (comment)

Author: AviVahl

package.json

@@ -6,6 +6,7 @@
   "main": "./build/engine.io.js",
   "types": "./build/engine.io.d.ts",
   "exports": {
+    "types": "./build/engine.io.d.ts",
     "import": "./wrapper.mjs",
     "require": "./build/engine.io.js"
   },