build: replace Travis by GitHub Actions

.github/workflows/build.yml

@@ -0,0 +1,31 @@
+name: Build
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: 26 8 4 * *
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+        node_version:
+          - 8
+          - 10
+    name: Node ${{ matrix.node_version }} on ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
+        with:
+          node-version: ${{ matrix.node_version }}
+      - run: >
+          sudo apt -qy update;
+          sudo apt -qy install libavahi-compat-libdnssd-dev libjpeg-turbo-progs optipng gifsicle
+        if: ${{ matrix.os == 'ubuntu-latest' }}
+      - run: npm install -g grunt-cli bower
+      - run: npm install        # this also includes "grunt dist"
+      - run: npm test