build: Replace Travis CI with GitHub Actions

Travis CI is no longer used for this project. The builds have been migrated to GitHub Actions.

This commit removes the .travis.yml file and updates the README.md to point to the GitHub Actions workflows.

Author: chaifeng

.travis.yml

@@ -1,7 +1,8 @@
 To Fix The Docker and UFW Security Flaw Without Disabling Iptables
 ==================
 
-[![Build Status](https://travis-ci.org/chaifeng/ufw-docker.svg)](https://travis-ci.org/chaifeng/ufw-docker)
+[![Build and Push Images](https://github.com/chaifeng/ufw-docker/actions/workflows/build.yml/badge.svg)](https://github.com/chaifeng/ufw-docker/actions/workflows/build.yml)
+[![Unit Testing ufw-docker](https://github.com/chaifeng/ufw-docker/actions/workflows/testing.yml/badge.svg)](https://github.com/chaifeng/ufw-docker/actions/workflows/testing.yml)
 [![chaifeng/ufw-docker-agent](https://img.shields.io/docker/pulls/chaifeng/ufw-docker-agent)](https://hub.docker.com/r/chaifeng/ufw-docker-agent)
 
 - [English](#tldr)