Fix leetcode-cn urls

It seems the leetcode-cn plugin need one more url replaced for working well.
That is config.sys.urls.problem_detail

Author: zouyonghao

plugins/leetcode.cn.js

@@ -15,6 +15,7 @@ plugin.init = function() {
   config.sys.urls.problems        = 'https://leetcode-cn.com/api/problems/$category/';
   config.sys.urls.problem         = 'https://leetcode-cn.com/problems/$slug/description/';
   config.sys.urls.graphql         = 'https://leetcode-cn.com/graphql';
+  config.sys.urls.problem_detail  = 'https://leetcode.com/graphql';
   config.sys.urls.test            = 'https://leetcode-cn.com/problems/$slug/interpret_solution/';
   config.sys.urls.session         = 'https://leetcode-cn.com/session/';
   config.sys.urls.submit          = 'https://leetcode-cn.com/problems/$slug/submit/';