Add GitHub Actions Workflow

.github/workflows/ci.yml

@@ -0,0 +1,34 @@
+name: CI
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby:
+          - 2.3
+          - 2.4
+          - 2.5
+          - 2.6
+          - 2.7
+          - '3.0'
+          - 3.1
+          - head
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - name: rubocop
+        run: bundle exec rubocop
+      - name: test
+        run: bundle exec rake test
+        continue-on-error: ${{ matrix.ruby == 'head' }}