Migrate to Github Actions

Author: exoego

Diff for: .github/workflows/ci.yaml

@@ -0,0 +1,31 @@
+name: scala-lang docs
+
+on:
+  pull_request:
+  schedule:
+    - cron: '00 0 * * *'
+
+jobs:
+  foo:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '2.5.8'
+          bundler-cache: true
+      - name: Build documents
+        run: |
+          bundle exec jekyll build 2> error.log
+          cat >&2 error.log
+          ( ! grep -qie Error -e Warn error.log )
+          find ./_site \( -type d \( -name events -o -name training \) -prune -false \) -o \( -type f ! -name error.log -empty \)
+          find ./_site \( -type d \( -name events -o -name training \) -prune -false \) -o \( -type f ! -name error.log -empty \) | ( ! read )
+      - name: Proofing (Pull Request)
+        if: ${{ github.event_name != 'schedule' }}
+        run: |
+          bundle exec htmlproofer ./_site/ --disable-external --only-4xx --empty-alt-ignore --allow-hash-href
+      - name: Proofing (Cron)
+        if: ${{ github.event_name == 'schedule' }}
+        run: |
+          bundle exec htmlproofer ./_site/ --external_only --only-4xx --http-status-ignore "400,401,429" --empty-alt-ignore --allow-hash-href --url-ignore "/trends.google.com/,/pgp.mit.edu/,/www.oracle.com/"