upgrade GMA min version badge

Author: github-paul-nicolas

README.md

@@ -10,7 +10,7 @@ If you want to display Teads ads in your iOS application through AdMob mediation
 
 - ![Platform: iOS 10+](https://img.shields.io/badge/Platform-iOS%2010%2B-blue.svg?style=flat)
 - ![Xcode: 12.5+](https://img.shields.io/badge/Xcode-12.5+-blue.svg?style=flat)
-- ![GoogleMobileAdsSDK: 9.0+](https://img.shields.io/badge/GoogleMobileAdsSDK-8.0+-blue.svg?style=flat)
+- ![GoogleMobileAdsSDK: 9.0+](https://img.shields.io/badge/GoogleMobileAdsSDK-9.0+-blue.svg?style=flat)
 - ![Teads SDK: 5.0.3+](https://img.shields.io/badge/Teads%20SDK-5.0.3+-blue.svg?style=flat)
 
 - ✅  Displaying Teads banners