refactor: code

Author: alexander-akait

lib/Server.js

@@ -252,7 +252,7 @@ class Server {
     const historyApiFallback = require('connect-history-api-fallback');
 
     const options =
-      typeof this.options.historyApiFallback !== 'undefined'
+      typeof this.options.historyApiFallback !== 'boolean'
         ? this.options.historyApiFallback
         : {};