Add github actions workflow

.github/workflows/ruby.yml

@@ -0,0 +1,19 @@
+name: Test
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+      uses: ruby/setup-ruby
+    - name: Install dependencies
+      run: bundle install
+    - name: Run tests
+      run: bundle exec rake