Update README.md

Author: fpistm

README.md

@@ -5,7 +5,7 @@
 
 [![GitHub release](https://img.shields.io/github/release/stm32duino/Arduino_Core_STM32.svg)](https://github.com/stm32duino/Arduino_Core_STM32/releases/latest)
 ![GitHub All Releases](https://img.shields.io/github/downloads/stm32duino/Arduino_Core_STM32/total.svg?label=downloads%20since%201.4.0)
-[![GitHub commits](https://img.shields.io/github/commits-since/stm32duino/Arduino_Core_STM32/1.8.0.svg)](https://github.com/stm32duino/Arduino_Core_STM32/compare/1.9.0...master)
+[![GitHub commits](https://img.shields.io/github/commits-since/stm32duino/Arduino_Core_STM32/1.9.0.svg)](https://github.com/stm32duino/Arduino_Core_STM32/compare/1.9.0...master)
 <!-- [![Build Status](https://travis-ci.com/stm32duino/Arduino_Core_STM32.svg?branch=master)](https://travis-ci.com/stm32duino/Arduino_Core_STM32) -->
 
 * [Introduction](https://github.com/stm32duino/Arduino_Core_STM32#Introduction)<br>