AlertPlugin need haik original class name "haik-plugin-alert"

I pull-requested implement AlertPlugin #46 .
But haik original class name "haik-plugin-alert" is needed when return html.

So, I will add this change soon.
Changes maybe like this : 

## before
```php
'<div class="alert alert-warning">'.\Parser::parse('test').'</div>'
```

## after
```php
'<div class="haik-plugin-alert alert alert-warning">'.\Parser::parse('test').'</div>'
```