README: update arduino board definition link

Author: proppy

README.md

@@ -7,8 +7,8 @@ This sample shows how to call [Firebase](https://www.firebase.com/) from the [ES
 ## Requirements
 
 - 1 [ESP8266 Arduino board](https://www.adafruit.com/products/2821).
-- [Arduino 1.6.x](https://www.arduino.cc/en/Main/Software)
-- ESP8266 Arduino board definition [(master branch)](https://github.com/esp8266/Arduino#using-git-version-) or [install stable with Boards Manager](https://github.com/esp8266/Arduino#installing-with-boards-manager)
+- [Arduino 1.6.7](https://www.arduino.cc/en/Main/Software)
+- [ESP8266 Arduino board definition](https://github.com/esp8266/Arduino#installing-with-boards-manager)
 
 ## Setup