mix.options is not a function

I've been trying to run PurifyCSS for my Laravel app, but keep getting the "mix.options is not a function" error whenever I run 'gulp' from the command line. mix.styles works just fine though

I understand that this problem happened for a lot of people because they were on old versions of Laravel mix, however I believe I've updated it (eg npm laravel-mix -v returns "3.10.10")

Any advice? Thanks

var elixir = require('laravel-elixir');

elixir(function(mix) {
mix.options({ purifyCss: true });
mix.styles([
    'bootstrap.css',
    'cc.css'
]);
});

via Chebli Mohamed