fix: Add std/portable to list of package exports (#1605)

Author: chances

NOTICE

@@ -32,6 +32,7 @@ under the licensing terms detailed in LICENSE:
 * forcepusher <bionitsoup@gmail.com>
 * Piotr Oleś <piotrek.oles@gmail.com>
 * Saúl Cabrera <saulecabrera@gmail.com>
+* Chance Snow <git@chancesnow.me>
 
 Portions of this software are derived from third-party works licensed under
 the following terms:

package.json

@@ -46,6 +46,7 @@
   "types": "index.d.ts",
   "exports": {
     ".": "./index.js",
+    "./std/portable": "./std/portable/index.js",
     "./lib/loader": {
       "import": "./lib/loader/index.js",
       "require": "./lib/loader/umd/index.js"