Alert css3 animation docs update for PR #4573

Updated docs to reflect changes in PR #4573
TODO: The following example of alert in docs needs to be changed
```
Configure on the fly

New to Foundation 5, you can now reconfigure instances of your plugin after the page has loaded and Foundation has already been initialized.

Lets pretend that we have an alert that was on our page when Foundation was first initialized:
HTML

<div data-alert class="alert-box" id="myAlert"> This is a standard alert. <a href="#" class="close">&times;</a> </div>

The default fade out speed is 300 miliseconds, if we wanted to change this to 3 seconds we could do the following:
JS

$('#myAlert').foundation({alert: {speed: 3000}});

You can set any configuration option or callback this way.
```