feat: update package.json exports (#249)

* fix: add fallback `./*` -> `./*.js` export

This allows us to `import` or `require` from any arbitrary entry point without breaking the overrides above it.

Currently, for instance, it is not possible to do `import { validateCartItems } from 'use-shopping-cart/utilities/serverless'`. This is fixed by this PR.

* chore: `./utilities/*` to JS source files, `./*` to dist TS output

use-shopping-cart/package.json

@@ -27,7 +27,9 @@
     "./utilities": {
       "require": "./utilities/serverless.js",
       "node": "./utilities/serverless.js"
-    }
+    },
+    "./utilities/*": "./utilities/*.js",
+    "./*": "./dist/*.js"
   },
   "engines": {
     "node": ">=8",