Add CI to unit test and validate compatibility

Using `fetch-depth: 0` on checkout because the code relies on the
history of the repository

.github/workflows/build.yml

@@ -0,0 +1,29 @@
+name: Build
+
+on: [push]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-java@v2
+        with:
+          distribution: 'adopt'
+          java-version: '11'
+      - run: ./gradlew check --console=plain
+
+  compatibility:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-java@v2
+        with:
+          distribution: 'adopt'
+          java-version: '11'
+      - run: ./gradlew assemble --console=plain
+      - run: java -jar app/build/libs/app.jar