[feature] replace travis ci with github actions

.github/workflows/ci.yml

@@ -0,0 +1,14 @@
+name: Build
+on: [push, pull_request]
+jobs:
+  build:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up JDK 8
+        uses: actions/setup-java@v3
+        with:
+          java-version: '8'
+          distribution: 'temurin'
+      - name: Build with Maven
+        run: mvn clean test

README.md

@@ -1,5 +1,5 @@
 # TEI-Authorizer
-[![Build Status](https://travis-ci.org/BCDH/TEI-Authorizer.png?branch=master)](https://travis-ci.org/BCDH/TEI-Authorizer) [![Java 7+](https://img.shields.io/badge/java-7+-4c7e9f.svg)](http://java.oracle.com) [![License GPL 2](https://img.shields.io/badge/license-GPL%202-blue.svg)](https://www.gnu.org/licenses/gpl-2.0.html) [![Download](https://img.shields.io/badge/download-version%201.0-ff69b4.svg)](http://search.maven.org/remotecontent?filepath=org/humanistika/oxygen/tei-authorizer/1.0/tei-authorizer-1.0-oxygen-plugin.jar)
+![Build Status](https://github.com/BCDH/TEI-Authorizer/actions/workflows/ci.yml/badge.svg) [![License GPL 2](https://img.shields.io/badge/license-GPL%202-blue.svg)](https://www.gnu.org/licenses/gpl-2.0.html) [![Download](https://img.shields.io/badge/download-version%201.0-ff69b4.svg)](http://search.maven.org/remotecontent?filepath=org/humanistika/oxygen/tei-authorizer/1.0/tei-authorizer-1.0-oxygen-plugin.jar)
 
 TEI Authorizer is a highly customizable plugin for [oXygen XML Editor](http://www.oxygenxml.com) which lets you: a) query remote authority files via HTTP and use retrieved data to autocomplete attribute values in your TEI documents; and b) define and implement forms to fill out new data and post it to your server via HTTP — all this from the comfort of your favorite XML editor.