migrate CI to GitHub Actions

get rid of travis
test against php 8.0 and 8.1

Author: Sergiy Petrov

.github/workflows/run-tests.yml

@@ -0,0 +1,41 @@
+name: run-tests
+
+on: [ push, pull_request ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: true
+      matrix:
+        php: ["5.6", "7.0", "7.1", "7.2", "7.3", "7.4", "8.0", "8.1"]
+
+    name: php-${{ matrix.php }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+
+      - name: Validate composer.json and composer.lock
+        run: composer validate --strict
+
+      - name: Cache Composer packages
+        id: composer-cache
+        uses: actions/cache@v2
+        with:
+          path: vendor
+          key: ${{ matrix.php }}-php-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ matrix.php }}-php-
+
+      - name: Install dependencies
+        run: composer update --no-interaction --prefer-dist --no-progress
+
+      - name: Execute tests
+        run: vendor/bin/phpunit --bootstrap vendor/autoload.php tests