fix blog title not updating in nav menu

closes #5474
- sets the blogTitle property of config when the title setting is changed

app/controllers/settings/general.js

@@ -3,6 +3,7 @@ import randomPassword from 'ghost/utils/random-password';
 
 export default Ember.Controller.extend({
     notifications: Ember.inject.service(),
+    config: Ember.inject.service(),
 
     selectedTheme: null,
 
@@ -51,9 +52,11 @@ export default Ember.Controller.extend({
 
     actions: {
         save: function () {
-            var notifications = this.get('notifications');
+            var notifications = this.get('notifications'),
+                config = this.get('config');
 
             return this.get('model').save().then(function (model) {
+                config.set('blogTitle', model.get('title'));
                 notifications.showSuccess('Settings successfully saved.');
 
                 return model;