fix: missing yargs.mjs

Due to the `yargs.mjs` file not being published, the fix merged with yargs#2151 is not effective yet. This change should fix that.

```
Cannot find module './node_modules/yargs/yargs.mjs' imported from ./cli.js
```

Author: hongaar

package.json

@@ -43,6 +43,7 @@
     "helpers/*",
     "index.mjs",
     "yargs",
+    "yargs.mjs",
     "build",
     "locales",
     "LICENSE",