Don't include ES6 module versions in npm package

The npm package is supposed to be for CommonJS usage, so only package
that to avoid confusion. This has become an issue now that nodejs
supports ES6 modules, where users are accidentally trying to import the
wrong files and get errors.

package.json

@@ -14,9 +14,7 @@
     "VERSION",
     "docs/API.md",
     "docs/LIBRARY.md",
-    "docs/LICENSE*",
-    "core",
-    "vendor/pako"
+    "docs/LICENSE*"
   ],
   "scripts": {
     "lint": "eslint app core po/po2js po/xgettext-html tests utils",