chore: refactor gitlab integration to github actions

Closes #25

Author: Steffen Giers

.github/workflows/php.yml

@@ -0,0 +1,20 @@
+name: PHP Composer
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Validate composer.json and composer.lock
+        run: composer validate
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress --no-suggest
+
+      - name: Run test suite
+        run: composer run-script test

.gitlab-ci.yml

@@ -26,5 +26,8 @@
     "require-dev": {
         "phpunit/phpunit": "^8",
         "spatie/phpunit-watcher": "dev-master"
+    },
+    "scripts": {
+        "test": "phpunit --bootstrap vendor/autoload.php tests"
     }
 }