Migrate the CI to GitHub Actions.

Disable jsdom 16.x in the process, because it seems to be broken.
This will need to be repaired afterwards.

Author: sjrd

.github/workflows/ci.yml

@@ -0,0 +1,34 @@
+name: CI
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        scalaversion: ["2.11.12", "2.12.10", "2.13.1"]
+        jsdomversion: ["10.0.0"] # TODO: add "16.0.0"
+    steps:
+      - uses: actions/checkout@v2
+      - uses: olafurpg/setup-scala@v10
+        with:
+          java-version: "[email protected]"
+      - uses: coursier/cache-action@v5
+      - name: Use Node.js 12
+        uses: actions/setup-node@v1
+        with:
+          node-version: 12
+      - name: Install jsdom
+        run: npm install "jsdom@${{ matrix.jsdomversion }}"
+      - name: Unit tests
+        run: sbt "++${{ matrix.scalaversion }}" scalajs-env-jsdom-nodejs/test
+      - name: Doc generation
+        run: sbt "++${{ matrix.scalaversion }}" scalajs-env-jsdom-nodejs/doc
+      - name: Integration tests
+        run: sbt "++${{ matrix.scalaversion }}" test-project/run test-project/test