Fix build badge

Not sure why this no longer works, but changing it to use the filename instead of the action name seems to fix it.

Author: dmadison

README.md

@@ -1,5 +1,5 @@
 # Servo Input Library
-[![arduino-library-badge](https://www.ardu-badge.com/badge/ServoInput.svg?)](https://www.ardu-badge.com/ServoInput) [![Build Status](https://github.com/dmadison/ServoInput/workflows/build/badge.svg?branch=master)](https://github.com/dmadison/ServoInput/actions?query=workflow%3Abuild)
+[![arduino-library-badge](https://www.ardu-badge.com/badge/ServoInput.svg?)](https://www.ardu-badge.com/ServoInput) [![Build Status](https://github.com/dmadison/ServoInput/actions/workflows/ci.yml/badge.svg?branch=master)](https://github.com/dmadison/ServoInput/actions?query=workflow%3Abuild)
 
 This is an Arduino library that allows you to read the position of servo motors via their signal wire without delay. You can use this library to read RC receiver channels, find the motor positions of robotics, or debug other servo motor projects.