chore(package): explicitly declare js module type (#121)

Author: Fdawgs

package.json

@@ -3,6 +3,7 @@
   "version": "3.4.0",
   "description": "A small utility, used by Fastify itself, for generating consistent error objects across your codebase and plugins.",
   "main": "index.js",
+  "type": "commonjs",
   "types": "types/index.d.ts",
   "scripts": {
     "lint": "standard",