Remove Travis CI remnants

Author: marcelstoer

.travis.yml

@@ -1,7 +1,7 @@
 # NodeMCU 3.0.0
 
 [![Join the chat at https://gitter.im/nodemcu/nodemcu-firmware](https://img.shields.io/gitter/room/badges/shields.svg)](https://gitter.im/nodemcu/nodemcu-firmware?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-[![Build Status](https://travis-ci.org/nodemcu/nodemcu-firmware.svg)](https://travis-ci.org/nodemcu/nodemcu-firmware)
+[![CI](https://github.com/nodemcu/nodemcu-firmware/actions/workflows/build.yml/badge.svg)](https://github.com/nodemcu/nodemcu-firmware/actions/workflows/build.yml)
 [![Documentation Status](https://img.shields.io/badge/docs-release-yellow.svg?style=flat)](http://nodemcu.readthedocs.io/en/release/)
 [![License](https://img.shields.io/badge/license-MIT-blue.svg?style=flat)](https://github.com/nodemcu/nodemcu-firmware/blob/release/LICENSE)