Migrate the CI to GitHub Actions.

Author: sjrd

Diff for: .github/workflows/ci.yml

@@ -0,0 +1,25 @@
+name: CI
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        scalaversion: ["2.10.7", "2.11.12", "2.12.8", "2.13.0"]
+    steps:
+      - uses: actions/checkout@v2
+      - uses: olafurpg/setup-scala@v10
+        with:
+          java-version: "[email protected]"
+      - uses: coursier/cache-action@v5
+      - name: Build
+        run: sbt "++${{ matrix.scalaversion }}" scalajs-stubs/publishLocal
+      - name: MiMa
+        run: sbt "++${{ matrix.scalaversion }}" scalajs-stubs/mimaReportBinaryIssues