update gemini API key (#8)

Author: khanhnwin

genkit_flutter_agentic_app/genkit_backend/src/config.js

@@ -1,5 +1,5 @@
-const GOOGLE_API_KEY = process.env.GOOGLE_API_KEY;
+const GEMINI_API_KEY = process.env.GEMINI_API_KEY;
 const OPEN_WEATHER_API_KEY = process.env.OPEN_WEATHER_API_KEY;
 const UNSPLASH_ACCESS_KEY = process.env.UNSPLASH_ACCESS_KEY;
 
-export { GOOGLE_API_KEY, OPEN_WEATHER_API_KEY, UNSPLASH_ACCESS_KEY };
+export { GEMINI_API_KEY, OPEN_WEATHER_API_KEY, UNSPLASH_ACCESS_KEY };