[doc] filter() helper, bad key in example

[freezed]

Hi There's mistakes in the filter() helper documentation page.

In the second code example, the app.filters. keys have to replaced by helpers.filters.

In these lines:

Atomik::set('app.filters.required_message', 'You forgot to fill the %s field!');
(...)
Atomik::flash(Atomik::get('app.filters.messages'), 'error');

Hope it will helps