fix readme

Author: ladyada

README.md

@@ -1,4 +1,5 @@
-Adafruit_NAU7802 [![Build Status](https://travis-ci.com/adafruit/Adafruit_NAU7802.svg?branch=master)](https://travis-ci.com/adafruit/Adafruit_NAU7802)
+Adafruit_NAU7802 [![Build Status](https://github.com/adafruit/Adafruit_NAU7802/workflows/Arduino%20Library%20CI/badge.svg)](https://github.com/adafruit/Adafruit_NAU7802/actions)
+
 ================
 
 <a href="https://www.adafruit.com/product/4226"><img src="assets/board.jpg?raw=true" width="500px"></a>