```php
'viewport'        => 'width=device-width, initial-scale=1.0, maximum-scale=1.0',
```
instead
```php
'viewport'        => 'width=device-width; initial-scale=1.0; maximum-scale=1.0;',
```

Its values must be comma separated
See [Using the viewport meta tag to control layout on mobile browsers](https://developer.mozilla.org/en-US/docs/Mobile/Viewport_meta_tag)