Update discord link (#1123)

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] Documentation Update

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

README.md

@@ -27,7 +27,7 @@
   <a href="https://ragflow.io/docs/dev/">Document</a> |
   <a href="https://github.com/infiniflow/ragflow/issues/162">Roadmap</a> |
   <a href="https://twitter.com/infiniflowai">Twitter</a> |
-  <a href="https://discord.gg/jEfRUwEYEV">Discord</a> |
+  <a href="https://discord.gg/4XxujFgUN7">Discord</a> |
   <a href="https://demo.ragflow.io">Demo</a>
 </h4>
 

README_ja.md

@@ -28,7 +28,7 @@
   <a href="https://ragflow.io/docs/dev/">Document</a> |
   <a href="https://github.com/infiniflow/ragflow/issues/162">Roadmap</a> |
   <a href="https://twitter.com/infiniflowai">Twitter</a> |
-  <a href="https://discord.gg/jEfRUwEYEV">Discord</a> |
+  <a href="https://discord.gg/4XxujFgUN7">Discord</a> |
   <a href="https://demo.ragflow.io">Demo</a>
 </h4>
 

README_zh.md

@@ -27,7 +27,7 @@
   <a href="https://ragflow.io/docs/dev/">Document</a> |
   <a href="https://github.com/infiniflow/ragflow/issues/162">Roadmap</a> |
   <a href="https://twitter.com/infiniflowai">Twitter</a> |
-  <a href="https://discord.gg/jEfRUwEYEV">Discord</a> |
+  <a href="https://discord.gg/4XxujFgUN7">Discord</a> |
   <a href="https://demo.ragflow.io">Demo</a>
 </h4>