quote attribute value in ^= selector in button.js

js/button.js

@@ -97,7 +97,7 @@
   // BUTTON DATA-API
   // ===============
 
-  $(document).on('click.bs.button.data-api', '[data-toggle^=button]', function (e) {
+  $(document).on('click.bs.button.data-api', '[data-toggle^="button"]', function (e) {
     var $btn = $(e.target)
     if (!$btn.hasClass('btn')) $btn = $btn.closest('.btn')
     $btn.button('toggle')