refactor: use import and require fields

Author: AndrewLeedham

package.json

@@ -5,7 +5,10 @@
   "author": "Mark <[email protected]>",
   "main": "index.js",
   "module": "index.mjs",
-  "exports": "./index.mjs",
+  "exports": {
+    "import": "./index.mjs",
+    "require": "./index.js"
+  },
   "scripts": {
     "benchmark": "node benchmark",
     "build": "rollup --config --failAfterWarnings",