Wrong flag-icon.css gets loaded, this file is changed to flag-icons.css in the latest components/flag-icon-css

This package uses components/flag-icons.

It works fine with v3.5.0 (https://packagist.org/packages/components/flag-icon-css#3.5.0) of this package, however, with newer versions the flag-icon.css has been renamed to flag-icons.css, resulting in a 404 when trying to load the flag icons.

I would suggest to either fix this by changing the flag-icon.css in this package to flag-icons.css, or lock the flag-icon-css package to 3.5.0.

Prerequisites

[x] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
[x] The issue still exists against the latest master branch of yii2-icons.
[x] This is not an usage question. I confirm having gone through and read the documentation and demos.
[x] This is not a general programming / coding question. (Those should be directed to the webtips Q & A forum).
[x] I have attempted to find the simplest possible steps to reproduce the issue.
[x] I have included a failing test as a pull request (Optional).

I include the latest yii2-icons.
I load the assets to the view via \kartik\icons\Icon::map($this);
I load the page, and it does a request to http://localhost:3001/assets/2cb9e3a/css/flag-icon.css , which doesn't exist. However, http://localhost:3001/assets/2cb9e3a/css/flag-icon**s**.css does exist.

When I follow those steps, I see... flag-icon.css gets loaded, which is incorrect when the latest components/flag-icons-css is used.

I was expecting... I expect the flag-icons.css to get loaded, which is the standard in the latest components/flag-icon-css package.