Switch to Github Actions for CI

.github/workflows/build.yml

@@ -0,0 +1,52 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        java-version:
+          - 1.8
+          - 9
+          - 10
+          - 11
+          - 12
+          - 13
+          - 14
+          - 15-ea
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Validate Gradle Wrapper
+        uses: gradle/wrapper-validation-action@v1
+
+      - name: Generate cache key
+        run: ./.github/workflows/checksum.sh checksum.txt
+
+      - uses: actions/cache@v2
+        with:
+          path: ~/.gradle/caches
+          key: ${{ runner.os }}-gradle-${{ matrix.java-version }}-${{ hashFiles('checksum.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-${{ matrix.java-version }}-
+
+      - name: Configure JDK
+        uses: actions/setup-java@v1
+        with:
+          java-version: ${{ matrix.java-version }}
+
+      - name: Test
+        run: ./gradlew build check
+
+      - name: Publish (default branch only)
+        if: github.ref == 'refs/heads/master' && matrix.java-version == '1.7'
+        run: ./gradlew uploadArchives
+        env:
+          ORG_GRADLE_PROJECT_SONATYPE_NEXUS_USERNAME: ${{ secrets.SONATYPE_NEXUS_USERNAME }}
+          ORG_GRADLE_PROJECT_SONATYPE_NEXUS_PASSWORD: ${{ secrets.SONATYPE_NEXUS_PASSWORD }}