fix(esm): add default export to maximize compat

Make it work with Jest

Fix #27

Author: gregberge

package.json

@@ -9,7 +9,8 @@
   "exports": {
     ".": {
       "import": "./dist/index.mjs",
-      "types": "./dist/index.d.ts"
+      "types": "./dist/index.d.ts",
+      "default": "./dist/index.mjs"
     }
   },
   "keywords": [