Fix broken discord link (#356)

### What problem does this PR solve?

Fix broken discord link


### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Documentation Update

README.md

@@ -187,7 +187,7 @@ See the [RAGFlow Roadmap 2024](https://github.com/infiniflow/ragflow/issues/162)
 
 ## 🏄 Community
 
-- [Discord](https://discord.gg/trjjfJ9y)
+- [Discord](https://discord.gg/4XxujFgUN7)
 - [Twitter](https://twitter.com/infiniflowai)
 
 ## 🙌 Contributing

README_ja.md

@@ -183,7 +183,7 @@ $ docker compose up -d
 
 ## 🏄 コミュニティ
 
-- [Discord](https://discord.gg/trjjfJ9y)
+- [Discord](https://discord.gg/4XxujFgUN7)
 - [Twitter](https://twitter.com/infiniflowai)
 
 ## 🙌 コントリビュート

README_zh.md

@@ -183,7 +183,7 @@ $ docker compose up -d
 
 ## 🏄 开源社区
 
-- [Discord](https://discord.gg/trjjfJ9y)
+- [Discord](https://discord.gg/4XxujFgUN7)
 - [Twitter](https://twitter.com/infiniflowai)
 
 ## 🙌 贡献指南