Fix publish options in bundle examples

[vjik]

Description

https://github.com/yiisoft/assets/blob/master/docs/guide/en/asset-bundles.md

Currently, examples are incorrect:

public array $publishOptions = [
    'only' => [
        'css/bootstrap.css',
        'js/bootstrap.js',
    ]
];

only option doesn't exist. filter should be used instead.