Migrate from Travis CI to GitHub Actions

.github/workflows/ci.yml

@@ -0,0 +1,33 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: Build Spark
+
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        java:
+          - 11
+          - 15
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Set up JDK ${{ matrix.java }}
+        uses: actions/setup-java@v1
+        with:
+            java-version: ${{ matrix.java }}
+
+      - name: Cache Maven packages
+        uses: actions/cache@v2
+        with:
+            path: ~/.m2
+            key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+            restore-keys: ${{ runner.os }}-m2
+
+      - name: Build with Maven
+        run: mvn --batch-mode --update-snapshots verify