Switch to GitHub Actions-based CI (#3)

Switch to GitHub Actions-based CI

Author: jparise

.github/workflows/ci.yml

@@ -0,0 +1,20 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Lint
+      run: |
+        php --version
+        find . -name "*.php" -print0 | xargs -0 -n1 php -l