Add Github action that checks formatting. (#1019)

Author: maciejwalkowiak

.github/workflows/build.yml

@@ -129,3 +129,17 @@ jobs:
           BRANCH: gh-pages
           FOLDER: build/docs/javadoc
           CLEAN: true
+          
+  check-formatting:
+    name: Check Formatting
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout 🛎️
+        uses: actions/checkout@v2.3.1
+      - name: set up JDK 1.8
+        uses: actions/setup-java@v1
+        with:
+          java-version: 1.8
+      - name: Check formatting with Spotless
+        run: |
+          ./gradlew spotlessJavaCheck spotlessKotlinCheck