doc: update badge version

Signed-off-by: Frederic Pillon <[email protected]>

Author: fpistm

README.md

@@ -1,5 +1,5 @@
 # Arduino_Tools
 [![GitHub release](https://img.shields.io/github/release/stm32duino/Arduino_Tools.svg)](https://github.com/stm32duino/Arduino_Tools/releases/latest)
-[![GitHub commits](https://img.shields.io/github/commits-since/stm32duino/Arduino_Tools/2.1.1.svg)](https://github.com/stm32duino/Arduino_Tools/compare/2.1.1...master)
+[![GitHub commits](https://img.shields.io/github/commits-since/stm32duino/Arduino_Tools/2.2.0.svg)](https://github.com/stm32duino/Arduino_Tools/compare/2.2.0...master)
 
 Contains upload tools for STM32 based boards and some other usefull scripts.