ci: add github action (#32)

Author: erezrokah

.github/workflows/test.yml

@@ -0,0 +1,26 @@
+name: Netlify Plugin Sitemap Test
+
+on:
+  push:
+    branches: [master]
+    tags: ['*']
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 10
+    strategy:
+      matrix:
+        os: [ubuntu-latest]
+        node-version: [14.x]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm ci
+      - run: npm test