Use GitHub Actions for building, refactor the builder configuration.

.github/workflows/build.yml

@@ -0,0 +1,29 @@
+name: Build/release
+
+on: push
+
+jobs:
+  release:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest, windows-latest]
+
+    steps:
+      - name: Check out Git repository
+        uses: actions/checkout@v1
+
+      - name: Install Node.js, NPM and Yarn
+        uses: actions/setup-node@v1
+        with:
+          node-version: 14
+
+      - name: Build/release Electron app
+        uses: samuelmeuli/action-electron-builder@v1
+        with:
+          github_token: ${{ secrets.github_token }}
+
+          # If the commit is tagged with a version (e.g. "v1.0.0"),
+          # release the app after building
+          release: ${{ startsWith(github.ref, 'refs/tags/v') }}