build: support modern node resolution (#172)

If tsconfig's moduleResolution is set to Node16 or NodeNext it stops
using the "types" property in package.json and, instead, relies on
"types" inside "exports".

This now supports both.

package.json

@@ -13,6 +13,7 @@
   ],
   "exports": {
     ".": {
+      "types": "./dist/index.d.ts",
       "require": "./dist/index.cjs",
       "default": "./dist/index.mjs"
     }