Fix GhostTab and GhostTabPane array dependencies

No issue
- TabPanes weren't finding their tab due to not listing all their dependencies in Ember.computed

ghost/admin/components/gh-tab-pane.js

@@ -6,7 +6,8 @@ var TabPane = Ember.Component.extend({
         return this.nearestWithProperty('isTabsManager');
     }),
 
-    tab: Ember.computed('tabsManager.tabs.@each', function () {
+    tab: Ember.computed('tabsManager.tabs.[]', 'tabsManager.tabPanes.[]',
+    function () {
         var index = this.get('tabsManager.tabPanes').indexOf(this),
             tabs = this.get('tabsManager.tabs');