优化Route类的domain方法

library/think/Route.php

@@ -101,8 +101,7 @@ class Route
             foreach ($domain as $key => $item) {
                 self::domain($key, $item, $option, $pattern);
             }
-        } else {
-            if ($rule instanceof \Closure) {
+        } elseif ($rule instanceof \Closure) {
             // 执行闭包
             self::setDomain($domain);
             call_user_func_array($rule, []);
@@ -117,7 +116,7 @@ class Route
         } else {
             self::$rules['domain'][$domain]['[bind]'] = [$rule, $option, $pattern];
         }
-        }
+
     }
 
     private static function setDomain($domain)