Replace Travis with Github Actions. Closes #23

.github/workflows/test.yml

@@ -0,0 +1,34 @@
+name: Test
+
+on:
+  push:
+
+  pull_request:
+
+jobs:
+  run:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php-versions: ['7.0', '7.1', '7.2', '7.3', '7.4']
+
+    name: PHP ${{ matrix.php-versions }} test
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ matrix.php-versions }}
+        extensions: mbstring, intl
+        ini-values: post_max_size=256M, short_open_tag=On
+        coverage: xdebug
+        tools: composer
+
+    - name: Composer install
+      run: composer install
+
+    - name: Run tests
+      run: vendor/bin/phpunit