demo(tabs): update demo to Bootstrap3

src/tabs/docs/demo.html

@@ -1,9 +1,9 @@
 <div ng-controller="TabsDemoCtrl">
   Select a tab by setting active binding to true:
   <br />
-  <button class="btn btn-small" ng-click="tabs[0].active = true">Select second tab</button>
-  <button class="btn btn-small" ng-click="tabs[1].active = true">Select third tab</button>
-  <button class="btn btn-small" ng-click="tabs[1].disabled = ! tabs[1].disabled">Enable / Disable third tab</button>
+  <button class="btn btn-default btn-sm" ng-click="tabs[0].active = true">Select second tab</button>
+  <button class="btn btn-default btn-sm" ng-click="tabs[1].active = true">Select third tab</button>
+  <button class="btn btn-default btn-sm" ng-click="tabs[1].disabled = ! tabs[1].disabled">Enable / Disable third tab</button>
   <hr />
 
   <tabset>
@@ -13,7 +13,7 @@
     </tab>
     <tab select="alertMe()">
       <tab-heading>
-        <i class="icon-bell"></i> Select me for alert!
+        <i class="glyphicon glyphicon-bell"></i> Select me for alert!
       </tab-heading>
       I've got an HTML heading, and a select callback. Pretty cool!
     </tab>