Docs: Fix broken link

The link for the 'Gemini API Reference' in `google-genai-chat.adoc`
was pointing to an old URL and resulted in a 404 error.

This commit updates the URL to the correct destination.

Signed-off-by: MoGreene <[email protected]>

Author: Mo-Greene

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/chat/google-genai-chat.adoc

@@ -11,7 +11,7 @@ This implementation provides two authentication modes:
 - **Gemini Developer API**: Use an API key for quick prototyping and development
 - **Vertex AI**: Use Google Cloud credentials for production deployments with enterprise features
 
-link:https://ai.google.dev/gemini-api/docs/reference[Gemini API Reference]
+link:https://ai.google.dev/api[Gemini API Reference]
 
 == Prerequisites