Your plunk needs angular-animate, which angular-strap depends on.
http://plnkr.co/hsqT3FLEjXwdnXrxn4hx
<script src="//ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular.min.js"></script>
<script src="//ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular-animate.min.js"></script>