fix: fix broken links (#151)

* fix: fix broken links

* Update README.md

---------

Co-authored-by: hsluoyz <hsluoyz@qq.com>

Author: Selflocking

CONTRIBUTING.md

@@ -6,7 +6,7 @@ This project adheres to the [Contributor Covenant 1.2.](https://www.contributor-
 
 ## Questions
 
-* We do our best to have un [up to date documentation](https://casbin.org/docs/en/overview)
+* We do our best to have un [up to date documentation](https://casbin.org/docs/overview)
 * [Stack Overflow](https://stackoverflow.com) is the best place to start if you have a question. Please use the [casbin tag](https://stackoverflow.com/tags/casbin/info) we are actively monitoring. We encourage you to use Stack Overflow specially for Modeling Access Control Problems, in order to build a shared knowledge base.
 * You can also join our [Discord](https://discord.gg/S5UjpzGZjN).
 

README.md

@@ -135,40 +135,40 @@ What Casbin does NOT do:
 
 ## Documentation
 
-https://casbin.org/docs/en/overview
+https://casbin.org/docs/overview
 
 ## Online editor
 
 You can also use the online editor (https://casbin.org/editor/) to write your Casbin model and policy in your web browser. It provides functionality such as ``syntax highlighting`` and ``code completion``, just like an IDE for a programming language.
 
 ## Tutorials
 
-https://casbin.org/docs/en/tutorials
+https://casbin.org/docs/tutorials
 
 ## Policy management
 
 Casbin provides two sets of APIs to manage permissions:
 
-- [Management API](https://casbin.org/docs/en/management-api): the primitive API that provides full support for Casbin policy management.
-- [RBAC API](https://casbin.org/docs/en/rbac-api): a more friendly API for RBAC. This API is a subset of Management API. The RBAC users could use this API to simplify the code.
+- [Management API](https://casbin.org/docs/management-api): the primitive API that provides full support for Casbin policy management.
+- [RBAC API](https://casbin.org/docs/rbac-api): a more friendly API for RBAC. This API is a subset of Management API. The RBAC users could use this API to simplify the code.
 
-We also provide a [web-based UI](https://casbin.org/docs/en/admin-portal) for model management and policy management:
+We also provide a [web-based UI](https://casbin.org/docs/admin-portal) for model management and policy management:
 
 ![model editor](https://hsluoyz.github.io/casbin/ui_model_editor.png)
 
 ![policy editor](https://hsluoyz.github.io/casbin/ui_policy_editor.png)
 
 ## Policy persistence
 
-https://casbin.org/docs/en/adapters
+https://casbin.org/docs/adapters
 
 ## Policy consistence between multiple nodes
 
-https://casbin.org/docs/en/watchers
+https://casbin.org/docs/watchers
 
 ## Role manager
 
-https://casbin.org/docs/en/role-managers
+https://casbin.org/docs/role-managers
 
 ## Examples
 
@@ -188,11 +188,11 @@ Priority | [priority_model.conf](https://github.com/casbin/casbin/blob/master/ex
 
 ## Middlewares
 
-Authz middlewares for web frameworks: https://casbin.org/docs/en/middlewares
+Authz middlewares for web frameworks: https://casbin.org/docs/middlewares
 
 ## Our adopters
 
-https://casbin.org/docs/en/adopters
+https://casbin.org/docs/adopters
 
 ## How to Contribute