add active class to css for buttons, write new spec for button, "use strict"

js/bootstrap-tabs.js

@@ -20,6 +20,8 @@
 
 !function( $ ){
 
+  "use strict"
+
   function activate ( element, container ) {
     container
       .find('> .active')
@@ -39,6 +41,7 @@
       , $ul = $this.closest('ul:not(.dropdown-menu)')
       , href = $this.attr('href')
       , previous
+      , $href
 
     if ( /^#\w+/.test(href) ) {
       e.preventDefault()