Can not build js/css assets with .version()

[Andrew Drake]

• Laravel CRM Version: 6.0
• PHP Version: 7.3

Description:

Attempting to run "npm run dev" gives he following error

`node:fs:487
handleErrorFromBinding(ctx);
^

Error: ENOENT: no such file or directory, open '/resources/assets/css/app.css'`

Steps To Reproduce:

mix.js('resources/js/app.js', 'resources/assets/js') .sass('resources/sass/app.scss', 'resources/assets/css') .version();