!150 修复管理员注销后token未被重置的Bug

Merge pull request !150 from 一半/debug

@@ -73,7 +73,7 @@ class Auth extends \fast\Auth
     public function logout()
     {
         $admin = Admin::get(intval($this->id));
-        if (!$admin) {
+        if ($admin) {
             $admin->token = '';
             $admin->save();
         }