Use Github Actions for deployment

.github/workflows/gradle.yml

@@ -0,0 +1,45 @@
+name: Deployment
+
+on: [push]
+
+jobs:
+  deploy:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+        include:
+         - os: ubuntu-latest
+           displayName: linux
+         - os: windows-latest
+           displayName: windows
+         - os: macOS-latest
+           displayName: macOS
+
+    runs-on: ${{ matrix.os }}
+    name: Deploy on ${{ matrix.displayName }}
+
+    steps:
+    - name: Checkout source
+      uses: actions/checkout@v1
+    - name: Set up JDK
+      uses: actions/setup-java@v1
+      with:
+        java-version: 11.0.4
+    - name: Build with Gradle
+      run: ./gradlew jlinkZip
+    - name: Save artifact
+      uses: actions/upload-artifact@master
+      with:
+        name: JabRef-${{ matrix.displayName }}
+        path: build/image
+    - name: Upload to build.jabref.org
+      uses: garygrossgarten/github-action-scp@release
+      with:
+        local: build/image.zip
+        remote: JabRef-${{ matrix.displayName }}.zip
+        host: build-upload.jabref.org
+        username: builds_jabref_org
+        privateKey: ${{ secrets.buildJabRefPrivateKey }}
+        port: 9922
+}
+