Duplication of last alert when dismissing an alert

[troxler]

When showing multiple alerts and adding animation, there is a very strange behavior when dismissing an alert. Somehow it completely removes the alert HTML that was dismissed but instead duplicates the last alert in the list.

Steps to reproduce:

• Add an animation to the alerts by using .alerts {transition: all 5000ms ease-out;}
• Add multiple alerts
• Dimiss the first alert

For example: Add the alerts info1 and info2. When dismissing info1 it is instantly removed from the HTML, but instead the DOM shows info2 and a duplicated info2.

Tested with angular 1.5.8 and angular-flash-alert 2.3.0.

This might be related to the fix of #21