Fix Swagger UI link (#627)

Author: ssarj

docs/plugins/openapi.md

@@ -155,7 +155,7 @@ The endpoint to expose OpenAPI documentation frontend
 OpenAPI documentation frontend between:
 
 - [Scalar](https://github.com/scalar/scalar)
-- [SwaggerUI](https://github.com/openapi-api/openapi-ui)
+- [SwaggerUI](https://github.com/swagger-api/swagger-ui)
 - null: disable frontend
 
 ## references